Different = badwrong. See the stranger, fear the stranger, hate the stranger, kill the stranger.

Some people, for whatever reason, are unable to cope with people who don’t fall into their ingroup. While this doesn’t apply to racial issues, I have the sense that a lot of the anti queer stuff is a result of them being scrubs. Not 100%, probably not even the majority, but there is a certain kind of venom that comes from, “Why do you get to, when I’ve lived my whole life suppressing it?!” A lot of such people may not even realize it, because they’ve buried it so deeply.