Texting harms grammatical ability.
Note: The debate should be impossible to accept. Please express interest in the comments section if interested. If you find a way to work around this, you automatically forfeit all seven points.
The full resolution is as follows: 'Resolved: Text messaging is harmful to grammatical ability.'
Text messaging: The exchange of short messages, mainly composed of text, between portable electronic devices
Grammatical ability: The ability to produce morphologically and syntactically accurate sentences and to judge the grammaticality of sentences.
1. Debate structure:
2. In general, all arguments should be posted inside the debate, but sources can also be provided in comments.
3. BOP is on Pro.
4. No trolling, semantics or kritiks.
5. If Con disagrees with any of these rules, he must inform me before accepting the debate so that they can be modified.
Texting practically forces its users to use bad grammar. Every text must be brief, both because the length of a text must be below 160 characters and because it is difficult to type long paragraphs using a smartphone keyboard, whether it's a touchscreen software keyboard or an old-fashioned hardware keyboard with only a few keys that sometimes necessitated pressing a key multiple times in order to get a desired character to be typed. With this imposed brevity, users have to use shorthands and contractions or even omit words entirely in order to convey anything meaningful. These methods used to shorten messages mean that they are rarely, if ever, composed of full sentences.
While people can occasionally dabble in writing grammatically incorrect sentence fragments from time to time without ruining their grammar skills, texting is different in that its ubiquity makes it far more dangerous to one's grammatical ability. For some children, tapping out improperly spelled words with a smartphone is the main way they communicate with their peers; face-to-face interactions have long been replaced with communication facilitated through technology. Being exposed mostly to the sentence fragments found in text messages means that children would get less exposure to proper grammar, and a person who is not exposed to proper grammar would not be able to learn grammatical rules, as learning happens through exposure. Even as an adult, one's grammatical skills can deteriorate over time through the lack of exposure that being obsessed with texting would entail.
Children, who are increasingly using texting to communicate with their peers, might be the worst hit. Without a lot of exposure to proper written texts, a child might not be able to distinguish between proper and improper grammer due to the fact that he has not read enough full sentences to understand English's syntactical rules. This means that children might begin to pick up improper grammar thinking that it is proper; they would begin to spell "a lot" as "alot", confuse "their" with "there", "were" with "where", and believe that one can join an arbitrarily long list of independent clauses into one single sentence with commas. Texting harms the children the most.
The above are simply conclusions that are easily derived from logical reasoning and anecdotal evidence; however, real scholarly research into the effects of texting does exist, and they suggest that texting can spell doom for the English language as we know it, torturing it through misspellings like "dilemna" and "alot". A Penn State University study suggests that tweens who text more end up with worse grammar, possibly due to them mimicking the other tweens' way of using text speak and not switching back to correct grammar when it is demanded,  while another study said that texting may harm the texter's ability to properly use morphemes. 
As you can see, I have shown that texting can be detrimental to one's ability to write properly, both through logic and through citing scholarly studies. As such, I think that it should be resolved that texting harms one's grammatical ability. If you habitually exercise your thumbs through texting, watch out: you might be doing yourself and your grammar skills a disservice.
C1) Lack of novelty
Texting is a recent invention. If it could be blamed for worsening grammatical ability, we would see a sharp drop in this ability after texting became mainstream. But this there has been no evidence of this: Falling literacy has been reported for generations, since at least 1921, with no evidence of a dramatic plunge after the introduction of text messages. Errors like 'would of' have been around for at least 200 years, and other errors like apostrophe elision have also been around the whole time: there is no evidence that texting aggravates this. (1)
Moreover, for many years way before the invention of texting, we have simplified the written language to facilitate speed, on media such as post-it notes. Scribes of the yesteryear employed extensive simplification schemes (1), as have those who used alphabetic shorthand systems. (2) Take this script, with a transliteration in standard English orthography on the left (complete with the missing words):
C2) Code-switching is possible and easy
Contrary to popular belief, correct grammar depends on the acceptability of a sentence in the speech community. (3) (4) If both parties in a text conversation agree that a construction is acceptable, it is correct in that particular dialect of English, and therefore grammatical in this context. To show that texting is detrimental to grammatical ability, it must be demonstrated that they will cloud the judgement of texters and compel them to utilise textspeak in contexts where standard English, rather than the texting dialect, is expected, such as formal letters and examinations.
Evidence shows that texters are very much aware of the contexts. Their pragmatic competence allows them to switch between textspeak and formal English, whichever is apposite in the situation. For example, contrary to conventional wisdom, the use of textspeak in examinations, which are mostly taken by the text-saavy youth, is extremely rare. All of the youths interviewed by David Crystal found the notion of using textspeak in examinations absurd and unheard of, and when textisms do appear in examinations, they are usually the result of carelessness or hurrying, rather than reflecting an overall inability to write properly. (1)
C3) Multiple independent studies show otherwise
Numerous empirical studies have shown positive or neutral correlations between texting skills or frequency and general literacy. (9) For example, Kemp (2010) noted that college students with more exposure to texting were better than or equal to their peers at producing and comprehending texts in standard English (as well as in textspeak). (7) Other studies have shown a positive correlation between texting use and reading ability or verbal reasoning (9), which is closely related to grammatical ability since it requires grammatical knowledge to parse syntactically correct sentences. (8)
In today's perhaps all-too-connected world, text messaging's effects on one's grammar have come into debate due to the fact that texts can be so full of abbreviations and misspellings that they are incomprehensible to a person who is not familiar with the conventions of texting. 25% of words in a text message are misspelled in some way; some of those words are incorrectly capitalized, while others are spelled phonetically.  The content of an average text message is far from what one would expect in proper writing.
In his round, con has raised several points that he claims demonstrate that there is no risk that texting would ruin somebody's grammar. They are as follows: firstly, that there are other already existing systems of abbreviation, secondly, that texters are easily able to switch back to proper grammar when necessary, and finally, that there is no existing evidence to suggest that text messaging can be a detriment to one's ability to write properly. Here in this debate, I shall set out to demonstrate that con's claims are false, and that existing fears over the potential risks of texting are legitimate.
Con claims that since texting is a recent invention, its introduction should be correlated with a sharp drop within the general population's grammatical ability. However, many factors can cause indicators of grammatical ability within the general population to fluctuate, so the lack of such a steep drop does not even come close to disproving anything about the relationship between texting and poor grammar. Proving the existence of a sharp decline within grammar scores is not necessary to proving that texting is harmful to grammar ability, as many factors in addition to texting can affect grammar scores. Con further argues that since abbreviation systems existed before texting, there is no harm to texting in terms of grammar skills. This is fallacious in that the fact that previous abbreviation systems exist does not say anything about the effects of texting.
Con made the argument that texters can switch between textspeak and normal writing with such ease that texting cannot affect their grammar skills. In reality, however, texters, especially those who are young, can have trouble with switching back to proper grammar after becoming accustomed to textspeak, and this is reflected in test scores. 
Con's argument that studies show no negative correlation between texting and grammar skills is contradicted by many studies which do show such a negative correlation; I have linked to them in my previous argument.
I thank my opponent for his arguments. My opponent presented three points in R1 before citing empirical studies that corroborate these claims. I will respond to these points one by one.
R1) Texting forces users to use bad grammar
My opponent asserts that texting obliges, and thus cultivates, bad grammar. Firstly, I challenge the premise of this statement. As I have written in the previous round, texting is not poor grammar. It is does utilise many forms of non-standard orthography (which is not, as per the definitions laid out in R1, encompassed by grammar, as it is not related to syntactic or morphological accuracy). However, texters do not use an 'ungrammatical' version of standard English. Textisms are grammatical in the 'dialect' of textspeak; textspeak simply isn't standard English. (2) Moreover, only around 6% of the text messages are abbreviated, according to Ling's Norwegian study of a text message corpus (1).
Contrary to my opponent's claims, developments in smartphone technology no longer necessitate the use of brief texts. Although a conventional mobile forces its users to use briefer texts because of the clumsiness of input, smartphone users can use functions like spellcheck and autocorrect to type in messages. For example, the Android system, which I use, allows me to type long, complex sentences which are grammatically and orthographically accurate. Furthermore, Whatsapp and Facebook Messenger don't limit the maximum length of a message. It must also be noted that 40% of text messages by women and 25% of text messages by men contain multiple sentences (1). This statistic was recorded in the old days; now, lifted restrictions and improved technology have likely racketed up this percentage.
To further test the claim that text messages are ungrammatical, I have taken a look at the first ten texts of DamnFunnyTexts.com. Most of them are complete sentences; in fact, complex hypertactic constructions like second conditionals are present. I have spotted no morphosyntactic errors, although nonstandard orthography was present. Texting does not increase exposure to poor grammar.
Finally, the validity of this argument hinges on the tenuous link between the putative ungrammaticality of text messaging and the use of non-standard forms of English where standard forms are expected. I will show in the other rebuttals that my opponent has failed to demonstrate this.
R2) Frequency of texting
Secondly, my opponent claims that the frequency of texting undermines grammatical ability because people learn to write grammatically through exposure to grammatically correct texts. There are several problems with this.
Firstly, texts do not decrease people's exposure to writing in Standard English. Even the most avid texter can peruse the works of renowned writers, past and present, as well as respectable periodicals like The Guardian, The Washington Post or The Daily Telegraph. One could argue that frequent texting decreases their exposure to reading high-quality texts because they have less time to invest in them, but the same can be said of computer gaming, sports, music or any other non-reading hobby. Unless we accept that these also cause poor grammar, we cannot say the same about texting.
Secondly, my opponent claims that increased exposure to sentence fragments in texts implies that children will get less exposure to proper grammar. However, sentence fragments are not ungrammatical. They are unacceptable in formal writing, but they still obey the syntactic rules of a language. For example, no native speaker would text ungrammatical fragments like these the ones with *:
(1) A: What did you do to my cakes?
B: Ate them/*I ate.
(2) A: How is he doing?
B: Better than he is/*Better than he's.
The first example shows that sentence fragments must be constituents (blocks of words functioning as a unit) in the syntax of a language, such as clause, verb phrase, etc. 'I ate' is a subject plus an transitive verb with no object, and not a constituent of the full sentence 'I ate the flowers', so native speakers do not write this. By contrast, 'ate them' is a verb phrase constituent, so native texters accept this. (3) The second text demonstrates that sentence fragments still obey grammatical rules: contractions are not allowed at the end of a sentence. Clearly, sentence fragments aren't poor grammar. If anything, they allow users to familiarise themselves with constituent groupings in the syntax of a language, as we have seen from (1).
The only possible deleterious effect of continued exposure to sentence fragments is the propensity to use them in formal texts. But even that is a dubious claim because there's another, far more common source of sentence fragments that dwarfs texting: Speech. If exposure to sentence fragments were indeed insidious, it would be speech, not texting, that is the main contributor. Of course, that is not true because writing is a learnt skill, and speech must precede the learning of writing.
R3) Children are texting more and more
Finally, my opponent claims that children had not had adequate exposure to written texts before texting, and may pick up improper grammar from there. However, all of the examples presented by my opponent were orthographical: they were either spelling problems (alot, their, etc.) or punctuation problems (comma splices). In fact, the 'alot' error demonstrates, if anything, grammatical competence: 'a lot', unlike other classifiers, has become a morphological atom, or morpheme, that has a single meaning (a large amount or very often). Texters confuse grammatical and orthographical words, and fail to separate 'a' and 'lot' by a space. An orthographical inaccuracy reveals underlying grammatical knowledge.
Moreover, my opponent claims that children have had no exposure to accurate grammar before they learn to text. Yet most of the grammar teaching occurs in the first few years of life; later education only plays a shaping role. For example, research has shown that practically no two- to four-year-olds make the error I showed in (2) above. Nor would most native English-speaking child produce sentences like 'You went there when?' or 'I you love' (which, incidentally, are grammatical in French) by the time they reach school age. Plus, as David Crystal points out, children learn to write before they learn to text. Only good writers are capable of texting. This is the reason why children who text are, empirically, better readers and writers (as shown in the study I cited last round). (1)
Finally, the errors my opponent cited do not come from texting. Texting does not compel people to write 'there' instead of 'their' (they involve the same number of keystrokes) or comma splices (most sentences in texts are short). One user on this site does not text, yet thought 'dilemma' was written 'dilemna' until correction by spellcheck (which, incidentally, texters have extensive exposure to). (5) Children cannot possibly pick up these errors from texting alone; the cause must be somewhere else. It is the skill of the English teacher and not the prevalence of texting that is responsible for these mistakes.
R4) Empirical evidence
My opponent cites two studies to support the above arguments. The first is rife with statistical and methodological inadequacies. Firstly, it was obvious to the participants that the study was about the effect of texting on grammar, which can lead to a small bias. Secondly, they seemed to be fishing for correlations: they demanded a motley of independent factors from the tweens, and the majority, e.g. total text messages, perceived usability of texting, television and music consumption, etc. had no effect on grammatical ability. The only significant factors found were grade and average sent adaptations. The latter, however, explains only 4.7% of the variance in grammar scores, an extremely small effect. Moreover, they only had 20 questions in their assessment, many of which tested orthography, not grammar: (7)
My opponent misinterpreted the second study. They did not study morpheme use but morphological awareness, a measure of metalinguistic ability. We use tacit grammatical knowledge when we write, so lower metalinguistic ability does not entail poorer grammatical competence. Here's an analogy: you don't need to know which muscles to move, as long as you can ride a bike.
They did record negative correlations between frequency of texting and texting adaptions, and reading. The probem is, they did not find non-texters for comparison. Texting may still have an overall positive correlation with reading ability, although suffering negative marginal returns with greater frequency. Textism use may be deleterious, but its effects may not override the positive effect of texting. Finally, the participants may also be biased: They were told about the purpose of the study, and given course credit for participation. No wonder the authors themselves only claimed that texting hurting grammar was a possibility. (7)
Sources in comments
Unfortunately I have to concede to con.:(
As my opponent has conceded, I will post no more arguments this round.
I thank my opponent for the meaningful debate, and hope we can engage in similar intellectual exchanges in the future.
Leugen9001 forfeited this round.