The thing I've only seen mentioned once or twice is that it's possible to write dialogue in which a character says something/racist/homophobic etc, without actually being that -ist oneself. Now, when privilege and isms are apparent in the way a piece is constructed (ie the recent SPN racefail fic) that's one thing. But having a character make such a remark does not equal the author believing that said character is right. (This doesn't even address the idea that two characters might have a relationship in which such joking is customary, much as some people in real life do, but I'm already TL;DR here.)