I agree with everything both
payn and
Charlaquin have said on this, but as an addendum I do also think there's something specific to D&Ders and quarreling. Let's face this: we're nerds, and when nerds fall to debating something nerdy (especially something nerdy that has no great ramifications outside its own nerdy domain), we, um...we can "get a little too into it."
My degree is not in psych, so I'm only guessing here, but my hunch is that a lot of how and why RPG nerds quarrel about RPGs and related stuff has to do with unconscious social dominance hierarchies. Humans are very driven by social hierarchies, and those of us who've been on the lower rungs of society's broader hierarchies, when we find a more accepting and inviting sub-culture hierarchy like among D&Ders, our energy to climb that social dominance ladder can get intense. I speak only for myself: the only way I've managed to avoid these behaviors is by becoming consciously aware of them and making an equally conscious decision not to indulge them. Where I let myself fall into these habits, I do fall.
Dirty Harry said it long ago:
"A man's got to know his limitations."