That's why I'm limiting my observation to forums that only lean one way. I know I oversimplified a bit, but when was the last time you saw a A&H poster threaten to kill themselves or try to get another fired from their jobs because they disagreed about videogames?
And even you noted that shit behaviour is only really limited to the political boards here. Whereas go to ResetERA or SomethingAwful and the constant political commisaring and emotional meltdowns are the rule, not the exception, on any thread about any subject. Look how many more rules ERA has compared to KF or ONA. I've also noticed the same thing on Facebook (where there are WAY more rightoids than you might expect, the Zucc allows hilariously racist things these days). Left-wing groups have a million rules and everyone threatens to kill themselves over stupid shit. Right-wing groups just laugh at the left and their rules seem to extend to "don't be a dickhead".
My personal theory is that leftists require authority whereas rightists believe in individual responsibility, at least in their online forms. Right-wingers tend to trust each other to behave, and if you don't behave, meh, that's your problem. But leftists must get an authority figure involved, and believe that people won't behave unless corralled.