I post on a female-dominated board that has many sub-fora, and in the ones that are not specifically devoted to religion, politics, abortion, breastfeeding, cloth diapering, child discipline (which may include spanking), and a few other controversial topics, those issues are banned beyond their mention.
But what is the topic that creates the most vicious debate?
On NFL/sports message boards: Tony Romo. He is fiercely defended by a few (including me) and fiercely ridiculed/attacked by many.
On military message boards: The F-35 fighter jet.
On the Board Game Geek forums, it’s “Ameritrash: good or bad?” (Ameritrash is a broad category of game. People argue about whether the category exists, whether games in that category are good or bad, and whether the term itself is good or bad.)
One reason why I stopped reading a few food-related forums was because arguments would go on for pages about whether one should use X or Y as a particular ingredient in a particular dish.
Food topics can be unusually volatile. My ex-wife is a member of the Slow Food movement which sounds fairly sane and benign on the surface but it is anything but that when you meet the leaders. It is a strongly militant organization that outdoes even the craziest of the breastfeeders. I only spoke to the leadership of the Slow Food movement a couple of times in person before I refused to ever do it again for fear of all of our safety (I was going to hurt them as badly as possible if we ever crossed paths again). If you think I am some sort of an arrogant ass, try cranking that up x1000 and then you have a remote approximation of how bad they are.