Facebook has opened up a mannerly can of worms for those of us who attempt to behave with utmost correct politeness at all times. None of the well-known etiquette mavens, as far as I know, have come up with a specific code of conduct for Facebook, and I think I understand why. There are different ways to view Facebook, and depending on how you view Facebook, the polite standard of behavior will change.
1. Facebook as a "neighborhood." In this scenario, Facebook is like a neighborhood street, and people's walls are like their homes. Anything you wish to post on your wall, therefore, is welcome and appropriate, and it is rude to ask people not to post those things, even things that may be offensive to you.
Problem: In a real home, what's in your house stays in your house. On Facebook, what's posted to your wall also gets posted to all of your friends' news feeds, so that when they call up their home page, "How Libertarians Will Kill Us All And Eat Our Young" is there whether they agree or not. However, you can block friends from your news feed, or de-friend them if the offense if strong enough.
Problem: It would be considered rude in the extreme to comment on things in people's actual homes in anything but the nicest way. If, for instance, I have a picture of myself with President Obama hung in my home, the only polite thing to say, even if you believe Obama is taking this country down in a socialism-fueled ball of flames, is "How nice for you!" On Facebook, however, people are SUPPOSED to comment on what you post. It's the whole point. So posting a picture of yourself with religious or political connotations is going to invite comment, which will lead to possibly heated discussion of a socially forbidden topic, which isn't polite.
2. Facebook is a big party, and what takes place on Facebook are just the kind of conversations that happen at the kind of big party where a lot of different types of people are gathered together.
Problem: Many. There are many, many ways to offend people in conversation, and all of them seem to exist on Facebook. There is misinterpretation, hot-button topics, carrying on conversations while excluding someone, discussing events in front of people who weren't invited...it's endless, really. If people view their walls as parties they themselves are hosting, then some sort of control can be attempted, but in my opinion it comes off as rude to attempt to tell people what they can and can't post. I've deleted posts on occasion when I felt they were inappropriate for my wall, but I've always felt badly about it, like I kicked a friend out of a party for cussing too loudly.
3. Facebook is a networking opportunity. Friend requests should be freely accepted unless there is a compelling reason not to, like an active restraining order.
Problem: Facebook is primarily social. We all have the right to decide who will be allowed to see our Facebook page. Some people genuinely don't care, which is fine, but the friction happens when someone who doesn't care attempts to friend someone who does. Some people have strict policies: not friending current students, supervisors, co-workers, sharks, or in-laws. That is absolutely their right; it can get exhausting trying to censor yourself so that everything you post is acceptable to everyone on your friend list.
I don't know the answer. I actually am not in favor for a formal codification of Facebook rules, because I think it's something that everyone uses differently.
Conclusion: Everyone needs to settle down. It's supposed to be fun! Unless you don't use it for fun! But still settle down!
Please, it's exhausting trying to fix all of you people.