I support trigger warnings. They aren't for avoiding offending people, they are so people who have genuine trauma (or just a strong wish to avoid certain sorts of content/storylines) can avoid those things. Having trigger warnings is much better than someone saying, "I don't read fantasy any more because there's too much violence against women." (Which someone has said to me, and honestly, I can't argue against. There's a lot. And it's not labelled.)
What's the difference between trigger warnings and asking someone if there's x, y or z in a book? (Which I see on GoodReads all the time.)
I mean, there's a whole WEBSITE for "does this movie contain x, y or z that I don't want to watch". (It's called "Does the dog die?" but it covers much more than that. I look at some of the things on the list and wonder why anyone needs to know that, but y'know what? It's not for me, and that's fine. There are allowed to be things in the world that make life better for people who aren't me.)
So, as an example: I have a friend with a strong needle/surgery phobia. As in, she has had therapy about it and she can faint having blood drawn or watching same on television. She pays attention to the warnings attached to media rating, and she asks friends if a book contains surgical or torture scenes. Yes, reading a medical scene triggers her phobia and makes her woozy.