When one reads about a particularly sick killer, it's hard not to wonder about the authors who sit around and dream these things up. (I often wonder the same thing about horror writers.) But it's not fair to judge authors or readers by these books.
I'm not sure why The Shining Girls got to me so much, maybe it was because the author didn't explain how her killer came to be the way he was. In other serial killer novels I've read, even Thomas Harris' Hannibal novels, the author delves into the killer's psychology. By giving the killer depth, their crimes don't just read as senseless, meaningless violence. I'm not sure why the distinction matters to me so much, but it does.