Do very many people do that? 'Cause, I've wondered.

I mean, kinkmemes. People complain a lot about things they bump into on kinkmemes. But I don't think I've ever seen a kinkmeme with a standardized warning system? (Actually, IIRC, the "Community" kinkmeme died because pairing and warning headers were required, so...there's that.)

I'm not disagreeing with you, I just think that fandom in general really likes to believe that people are whiny reactionaries who look for things to get offended about and thus no one has to take any complaint or criticism seriously. It's a thing that happens, all the time, on any side of any fandom argument. It's weird.