I'm not sure that's actually true.

I wouldn't say it is either but it is true that "discussing things to find out the truth" is actively advocated as a norm over "arguing to win". That makes a big difference. Enough that I only take breaks from lesswrong in disgust every couple of years whereas on, say, the MENSA discussion boards I have frequented my tolerance wears thin far more quickly. With 'debating as sparring' as the human default having active pressure against that tendency at least helps reduce the phenomenon to more tolerable levels without eliminating it.