I can't say I'm terribly sympathetic. I mean, I get that people have legitimate reasons for wanting to be warned about some things (like sex, drug abuse, suicide, etc.), but when you're making a laundry list of plot twists that will "ruin the story" for you, I think it's a little silly to expect the author to telegraph every possible thing that some readers might not like.
Or, a less extreme example: I'm a huge James/Lily fan. I find the perfect story, the first chapters are great... and then suddenly there's a Remus/Sirius side arc. It's not that I don't like slash or am intolerant or whatnot. It's just that a) I'm a huge lover of canon, and the author might not have considered an affair between the two AU (which I would), and b) I didn't expect this to happen since the story had no slash-tag, and it confuses me massively, because it doesn't fit the picture that I have of the story by this time.