On Less Wrong, people mostly seem to prefer "discussing things to find out the truth" instead of "arguing to win."

I'm not sure that's actually true.

The fact that so many LWers disengaged from Epiphany that she thinks she has never lost an argument strongly suggest that it is true (ETA: at least in some contexts), and also that the norm has a downside of making some newcomers highly overconfident. (I can't resist pointing out that a feature suggestion of mine probably would have helped here.)