I'm very for self moderation, being nice, etc, but at the same time i don't agree with heavier handed censorship and control, or blanket policies based more on the letter of the Law than the Spirit.
When you try to forcefully repress the shadow side of life, whether within self, others, a group, or what not, often it causes more problems in the long run. That negativity tends to go deeper and more unconscious, becomes more pathological and compulsive. Sure, on the surface things may "appear" nicer superficially, but the behind the scenes back biting, plotting, and vitriol goes deeper, underground and becomes more insidious and harder to directly transform.
It's sort of like prohibition. Worked real well. The underground, criminal mafia is a sort of symbol of what happens when the shadow side gets repressed too much. It goes underground, it gets more subtle, indirect and conniving and severe. Some of the worst forums (as far as interpersonal interactions) i've ever been on, are the New Age or Spiritual type ones wherein a lot of people have an attachment to maintaining or projecting a spiritual image, and you're supposed to be nice, loving, etc but lord help you if you go against the group think, you question, disagree with the moderators, etc. Such nice, spiritual groups can get real nasty, real quick, and groups or cliques gang up on individuals, but often in less obvious ways and more behind the scene ways. Again, it's due to too much repression of the shadow side. That side of life needs to be in the OPEN so it can get worked on in the light so to speak. Open conflict is not always a bad thing, sometimes it's needed for growth.
It's more a question of redirecting. One way for healthy redirection is for the more ethical, constructive, high minded type forum members to pay little attention to someone when they are acting in a non constructive way or to call them out on it. You don't have to completely ostracize them all the time (or overly focus on them as sometimes they are looking for that negative attention consciously or unconsciously), unless they consistently show themselves by actions to have no interest or inclination to work on themselves, or any concern for the larger good of the community.
And frankly, the huge majority of us, occasionally at some point have our off moments wherein we lose patience or centeredness and become more non constructive than is necessary or helpful to others, self or the community as a whole. We all make mistakes and mess up, and it's helpful to try to understand where someone is coming from and why they feel the way they do, before completely dismissing them.