General, mild spoiler for later seasons/episodes of Buffy:

Over time, it becomes evident that the people of Sunnydale are not completely ignorant of all the creepy supernatural stuff that goes on; it's more like one of those thing you Don't Talk About.

It's a shame that the horror stuff is a dealbreaker, 'cause it is a very good show, but I understand. I have a similar issue with icky medical stuff which makes it impossible for me to watch things like House.