Why do some viewers freak out over purposefully black flag mc's?

This is a genuine question. It came into my mid today watching Kinnporsche, and some of the comments and discussion I've seen around it. In BL's like Kinnporsche, The Wicked Game, etc, one of the main points of the show is that all or most of the characters are yellow flags at a minimum, most being red or black. I completely understand being disgusted by their actions, and fair criticism of the characters, but it's not like you go into watching those types of BL without knowing what you're getting into. Of course the main couple will still be together regardless of how toxic it gets, isn't that the whole point of the genre?