When you think about it, besides chat rooms, most of the forums are moderated, just how it is in IF. If one ventures to an anonymous bulletin board and expects courtesy, respect or even a decent treatment, then it might not be possible. It's not that people are not capable of it; its just that venting out without a moral/social filter attached between words that come to brain and fingers that type those words on keyboard, is much simpler. And they got nothing to lose.
Freedom of expression: Unfortunately, there is no such thing as "right" thing. There was this one bulletin board back in 2004-05 for X-Files where in hardcore fans fought tooth and nail with people who didn't believe in X-Files stuff. Fair enough. But people went as far as stalking them on other forums, cyber bullying and sometimes even thinly veiled death threats. The BB was closed when things went too far.
I know that one of the constant struggles as a forum moderator would be to balance things between what one might offensive vs. speaking out a point of view.
Can we talk about anything under the umbrella of freedom of expression?? I don't think so.