Keep Gay Marriage Illegal
Some people claim homosexuality is against evolution because the genes will not pass on. Yet it is precisely because it passes on in genes in a new way that could alter the dynamics of human genetic evolution that gay marriage is a bad idea.
The natural function of homosexuality in animals and in the history of human evolutionary development is to provide support for their nieces and nephews by NOT having kids of their own. It would be ridiculously intrusive for the government to insist homosexuals NOT have their own children and would harm many children if they couldn't adopt but should we really be promoting gay marriage which will necessarily lead to higher rates of homosexual child-raising? Do we really want to mess with the natural evolutionary role of the homosexual?
Nature is not equal. Think of all the various functions human beings must fill as a society. To make a human being capable of doing all of that would be impossible. There isn't brain, energy, or muscle space for that. Holding equality up as a sacred ideal is stupid, and would lead to the total breakdown of our ability to survive and continue as a race if followed to its logical extreme.
Make it equal, because it's right seems to be the rallying cry these days, but what of the many cases where equality is not the right way? We should be aware of the long-term consequences before we just march forward with new policies like gay marriage. Until we have some solid data showing what sort of changes will occur in human genetic makeup if gays pass on more genes it is reckless to legalize gay marriage.
I accept this debate. I will point out that I currently have no viewpoint on gay marriage, so I am going to see if I can support pro-gay marriage.
My opponent has basically a few points that he has made:
"The natural function of homosexuality in animals and in the history of human evolutionary development is to provide support for their nieces and nephews by NOT having kids of their own."
He has no proof of this so far. Plus, gay and lesbian parents are just as good as parents as heterosexual parents.
"Do we really want to mess with the natural evolutionary role of the homosexual?"
What evolutionary role? Besides, how can gays and lesbians reproduce? I ask my opponent to point out how.
Plus, I will point out that children thrive equally under both heterosexual and homosexual parents.
I await my opponent's response.
Not only in animals, but humans. Fa'afafine who are men who take on a third gender role in Samoa take on the role of a sort of "superuncle" in relation to their nieces and nephews. They do not have kids of their own.
As for evolutionary role, everything in human behavior has roots in evolution. To argue otherwise is to suggest people act in a vacuum. People's decisions are determined by their reaction to the environment surrounding the decision, what the individual has learned, and this is filtered through the individual's biological makeup which determines how the individual responds to that information. While biology is more than just genetics genetics ultimately is what guides the formation of the body through life.
Since all human behavior has roots in evolution we all have our own evolutionary role. When there is a group of people who share a behavioral characteristic like homosexuality there is an evolutionary reason for that. Science shows us this reason is to help take care of nieces and nephews rather than having kids of their own. The human population is already growing too fast. We should not promote homosexuals to reproduce through legalizing gay marriage.
Okay I am going to introduce my points for Same-Sex marriage.
C1: Social Equality
My opponent has said:
"As for evolutionary role, everything in human behavior has roots in evolution."
So my opponent says that sexual orientation is decided by genetics.
Marriage provides several advantages than being banned marriage. These include pensions, tax breaks, insurance coverage, social recognition, and better financial benefits. Why should gays/ lesbians be denied from this institution based soley on their sexuality? It's akin to the Jim Crow laws which denied African Americans the right to vote before the 1960s.
------Civil Rights and Constitutionality
Marriage has been concluded to be a basic civil right of man, and also concluded to be fundamental in our survival as a species. This was determined in Loving v. Virginia. Gay and lesbians should not be denied a fundamental human right when the cause is genetic like my opponent said. 
The result of the above case is from the Constitution. If marriage should be managed by the states, than it must be extended to them as well. This is because of the 14th amendment's Due Process and Equal Protection Clauses. Since my opponent and I have agreed that homosexuality is genetic and therefore not "chosen", this is due process, and because of the Equal Protection clause, a ban on gay marriage violates the Constitution. Therefore, SSM is Constitutional, and fulfills equal and excellent Civil Rights for all, instead of a few.
C2: Gay Marriage Harms/ Gains
John Stuart Mill has proposed a major philosophical principle: called the harm principle. Mill says:
" The actions of individuals should only be limited to prevent harm to other individuals." 
So, if gay marriage is not more harmful than beneficial, it should be legal.
Rebuttals to "harms"
My opponent has basically summed up his whole case as this:
"Science shows us this reason is to help take care of nieces and nephews rather than having kids of their own."
My opponent also voiced a concern on overpopulation.
However, the world population is expected to decline after 2070,  and in the USA birth rates are already falling, and has been for a while.  Your source also shows that the kind of people there that act as "super uncles" is common because of the Samoa culture of close families and tight-knit communities instead of the USA's culture of my individualism.
My opponent also has lacked to provide a source that gay marriage would lead to a lack of helping nieces and nephews by homosexual Uncles and Aunts.
Gains From Gay Marriage
Gay marriage leads to a range of different benefits:
1) Social recognition leading to stronger relationships with more meaning and status.
2) Gay marriage legalization would entitle homosexual couples equal financial benefits with heterosexual couples. This would be beneficial to the marriages, as well as local communities and the nation. Billions and more would be put in the economy. 
3) Helps children. Currently about a million children live in a household with homosexual parents. They are not harmed, as I will show soon, but if gay marriage was allowed, with all of the protections and benefits that come with Gay marriage legalization, many children would be helped as well. Would take many children out of adoption system.
4) Gay and lesbian parents are just as good as heterosexual parents. Numerous amonts of studies have proved this to be true, that children thrive equally under heterosexual and homosexual parents.    
Marriage is a fundamental human right. Under the Constitution, gay marriage should be legal. It comes with many social, economic, and psychological advantages, to all people. Plus, many more children would be helped with gay marriage being recognized.
MasturDbtor forfeited this round.
"Social Equality" is not worth the extinction of or any other evolutionary harm to the human race.
Allowing gay marriage will ultimately lead to more gay couples feeling more "normal" and hence free to use the IVF technology or even just sex for the sole purpose of having babies in order to reproduce.
It's OK to be gay, it's natural, but evolution's natural goal for homosexuals is to look after nieces and nephews for their brothers and sisters NOT to have kids of their own.
Parents are already feeling the pinch. With less gay family members to rely on to babysit more and more kids are thrown into day care centers, and families become more and more distanced from each other.
By not having their own kids and tending to needs of the greater good of the family as a whole homosexuals serve an honorable and noble social role, one which should be encouraged, not discouraged by encouraging homosexuals to get married.
"Allowing gay marriage will ultimately lead to more gay couples feeling more "normal" and hence free to use the IVF technology or even just sex for the sole purpose of having babies in order to reproduce."
Population is good. Plus, gay marriage legalization would only lead to about 0.6% more marriages in the whole USA 
"evolution's natural goal for homosexuals is to look after nieces and nephews for their brothers and sisters NOT to have kids of their own."
My opponent has failed to provide any evidence or sources of any of his claims. Gay Marriage would not lead to overpopulation, as the actual marriage rate would barely change, but allow social equality. There is no proof that "gay parents act as second parents to nephews and nieces". Denying gay marriage is violating a basic civil right, and my opponent has failed to rebut any of my arguments, while I have refuted my opponents' arguments.
"Population is good. Plus, gay marriage legalization would only lead to about 0.6% more marriages in the whole USA"
Population is not always "good". There are even concerns now about global overpopulation. Furthermore, it is not just about overall population growth or lackthereof but the dynamics of such growth. People fill many different social roles in society conditioned by evolution.
It is important that absent any compelling evidence that the result will be better that humans do NOT interfere with their own natural development by implementing policies that encourage people to stray away from their natural evolutionary function. Scientific evidence as I linked to in above posts clearly shows that human homosexuality is meant to be so that some members of human society can help take care of nieces and nephews, NOT so they can form families of their own.
By allowing gay marriage we are encouraging homosexuals to stray away from the natural model that has been given to us by evolution. It is OK that they are gay, but instead of trying to have kids of their own they should seek to be good uncles and aunts.
Allowing gay marriage will mean that more and more often gay couples will have kids of their own, spend more time with those kids, and hence less time looking after nieces and nephews. This changes the entire family dynamics. Whereas before their straight siblings and their spouses would get some necessary relief from parenting duties, allowing more investment of their time in productive work and social activities while making sure the kids still had adult supervision and bonding, now parents will increasingly find themselves on their own, their gay siblings preoccupied with their own children. Some of these parents will choose to cut back on work leading to less income, some on social and leisure activities leading to more stress, some will cut back on time with their children which will harm the children.
Furthermore as gays are evolutionarily conditioned for the role of supportive extra parent and now society is going to pressure them into becoming actual parents they will be taking on a weight they are not equipped for by nature, and the effects of this shift will likely be seen only later on in society.
My opponent has basically stated that Gay uncles are needed as a person to nurture the growth of the nieces and nephews. The only source he has is to defend this is instead about some strange people in American Samoa, where some Gay-like people who consider themselves of a "3rd sex", and they tend to help their newphews and nieces.
Furthermore, I have shown why Gay marriage should be legal, because of moral, and ethical reasons, and why marriage is a fundamental Civil Right (I proved these points too).
I think it is safe to say that legalizing gay marriage, which would only cause about 0.6% of the population to look for marriage (source in R4), would not be detrimental. I think it is safe to say that most families don't have a Gay uncle who watches the children and helps them.
My points were left unrefuted.