Could be wrong, but edgy jokes + Poe's Law (sarcasm is uncertain online) would be a strong attractant for actual * ists. They may use it all for plausible deniability cover, but I bet many don't even realize most posts are just joking and think they've discovered an underground movement of people like them. Either way, your outlook changes when you go from the only one with unpopular thoughts that you have to hide to one of an untold multitude in which you can freely express those thoughts and have them validated and reinforced.

An HN post 3mo back was insightful in this regard: https://news.ycombinator.com/item?id=19847437

What I don't know (and am interested to) is this: do * ists on such sites gain members mostly by other * ists finding the community or by converting trolls? Because those two pathways have very different antidotes.