For recent generations, I believe this has been the hardest lesson about social media. Before Facebook, people didn't seek out other people's profiles on the Internet to see what they were doing on-line. The Internet was faceless, you could be yourself or you could be someone else. I do not like it that employers use Facebook as a tool to judge possible employees, but understand why they do it.
When participating online, it's important to maintain some professional behavior. One reason is that your profile may potentially be viewed by a future boss, so it's important to maintain a positive image online, as much as you would in person. Additionally, while people want to feel free online, they need to act in such a way as to not hurt others' feelings and to behave in a way similar to how they would in person. Sometimes, people are too free to say things they want to say online, due to the relative anonymity of typing behind a computer monitor.
Social networking does allow for a lot of freedom of expression and may sometimes enhance creativity. However, things on the sites have gotten so sloppy that people are posting whatever comes to mind and showing photos that should probably not be seen. A professional standard would be good for everyone but it can not be enforced so it is not going to happen.
I think if you are a professional and you have a job or work at a company whose reputation might depend upon things that it's employees might say or do, then you should have the sense to keep things that might harm you are them private. If you want to have a facebook and post risque things, you should do so at your own risk and should probably keep the page private.
Yes, standards of professional behavior should be valued above freedom of expression on social networking sites, because it is still important to be nice to each other. People can find a way to get their point across without ad hominem attacks and without hurting feelings or bullying online. People can use social media while being professional.
The whole point of communication in American is the freedom to express ourselves as we see fit. Every website has standards of decorum. However, that doesn't mean everyone needs to be professional in how they carry themselves on various sites. On social networks especially, individual freedom of expression is the entire point of having those services in the first place.
I dont think it should be valued of freedom of expression because no matter what this is a free country and everyone should have the right to express themselves how they choose. There should be a certain limit on some things that are vulgar or are used as profanity but other than that people have that right to express themselves how they want