That's funny!
Well, as someone who has been in the middle of his share of controversy, this is how I see it:
Humans are a flocking species. They like to be a part of a group and message boards are a way of having a sense of comaradarie. It's a chance to be a part of a community and share similar opinions. But discussion groups sometimes offer controversial opinions -- which make things interested -- but new ideas challenge people to "leave the flock " so to speak, and they must then think for themselves.
Some people take a contrary opinion as a personal attack. It confronts their convictions, and that may make them feel less safe. They in turn, get defensive, and eventually offensive. Instead of debating the "idea" set forth, it's easier to attack the person who presented it.
Now, since humans are a flocking species, it's also natural to follow the "alpha dog." Very often the first person to start the antagonism is viewd as a "leader." He broke through. He made it easy for everyone to maintain their comfortable positions. Soon, more and more of them pile on to the upstart with a new point of view. Then it's a mob. Strength in numbers! But there's no reasoning with a mob. Everybody loses.
So in a sense, our little discussion group is a microcosm of society and societies throughout history -- from the crusades to the Salem witch hunts to the holocaust to the assassination of Martin Luther King, to Sept 11. People get pissed when other people think differently. And a small mind strikes back.
And so it goes.