My opinion of the worst part of the forum history (the breakup arc):
(my background with the forum first for perspective: I was a lurker for a long time, then, when I went to register, it happened to be during the time the mail server was misconfigured. I then continued to just lurk the forums, until finally I was able to register when the registration mail was fixed)
Normally, people trickle into a forum at a slow pace. As they slowly trickle in, they adjust to the existing atmosphere because they are a massive minority on the forum (people not yet acclimated).
But, with the large buildup of people who wanted to join, but were unable to (which by the way built up some huge annoyance, I was pretty annoyed about it myself, especially when I had sent several emails and such about it and was never even justified a response. I'm not reactionary though, so all I did was go, eh, whatever and move on with my life) coming in all at once, the atmosphere of the forum was somewhat chaotic due to the lower ratio of older members to new members than a forum usually has.
There wasn't an atmosphere for people to conform to like there was before and after that period in time.
Combine that with the older members getting very comfortable with a closed system, the moderation in this part of the forum being nearly nonexistent, and the arc that was going on in the comic at the time, and its really rather surprising it wasn't worse than it was.
I really don't even think of it as being about terrible people so much as a shit situation created by a lot of little factors added together to create a large problem.