When I first joined the Harry Potter fandom, I was kind of insanely anti-slash. This certainly had a bit to do with my über-religious upbringing—I just felt like slash didn't
belong in Harry Potter. I saw no signs of it in canon; HP was a children's book, really, and any kind of NC-17 fanfiction was just a bit too odd for my liking. Adding gay sex to the mix was just an extra squick.
It's kind of hilarious to look back now.
( My (tl;dr) thoughts on yaoi, let me show you them. )...Whoa, long entry is long. Sorry about that.