I'd suggest another guideline: keep your claims falsifiable.
The most heated online discussions I've witnessed have been around non-falsifiable claims. These discussions may offer an adrenaline rush for the participant, but not much else. Minds don't change in these discussions. Quite the opposite.
However, topics like religion are noteworthy in that none of the claims are falsifiable. Lots of political discussions (the more heated kind especially) deal in non-falsifiable claims.
PG suggests that such discussions can't happen around technical topics (JavaScript, baking?). I think there's evidence to the contrary on HN not to mention many other discussion forums.