There can be a very strict set of keywords, ones we all can agree carry a heavy condesending tone at the very least, that should be banned from facebook. Those keywords can help track the writer and identify him or her, let them be warned once and a lifetime ban on the second.
I totally support freedom of speech, and think that people should be able to speak their minds. However, I think there is a cut-off point. At some point, opinion just becomes hate, and the hate speech should not be allowed. Unfortunately, being able to say exactly where this cut-off point is becomes difficult. I think anything that is clear and evident hate should be banned, and other things taken care of on a case-by-case basis.
I think it is correct and I encourage Facebook to ban hate speech on its service. There are so many people using Facebook that there are problems that always happen when people use these kinds of speech to enflame even more an argument. Of course it is hard to differentiate but it is encouraged.
Now how can we classify "free speech" as such, when it is regulated? Hardly 'freedom of speech' at that point in time. If someone's feelings are so hurt to the point that it is impacting their lives, then perhaps it is best that they drop Facebook entirely. Quite frankly, someone's petty feelings do not excuse the infringement on the rights of others.
Facebook should not ban any type of speech. Even looking past the freedom of speech issue, hate, or other kinds of speech would be subjective. Where is the line drawn? I personally have chosen to unfriend people on facebook because of difference of opinion or the things that are said on their page, but I don't think they're posts needed to be banned as it wasn't directed at me personally. A feel a general opinion shouldn't be stifled as long as no one is forced to listen if they choose not to.