Human mind gets turned on by most twisted things they can imagine. Some people might deny it and try not to think about things like that and it works until you let your mind have crazy fantasies. Also people have different idea of crazy (some might feel really dirty and sick about things that are normal for some), but the main point is that the dark corner in your mind turns you on. Many times traumatic people or people who had not so safe childhood are more easily getting turned on by sick sexual fantasies - that does mean that "there's something wrong with you", but the thing that is wrong is not your fantasies or anything you should be ashamed of.
Just realize that it's normal to fantasize even about really sick things, and remember that:
1. Having a fantasy doesn't mean you want to do that in real life - you have choice.
2. Usually it's better to keep more hardcore fantasies away from real life, most of the time it will not play out well.
3. Everybody fantasize! Every person you have met today have fantasies, many of them really sick ones.
4. Don't stress too much about what kind of things turn you on. I've had fantasies about teachers, friends mom, sister, girlfriends little sister, getting humiliated, getting cheated, being controlled, old women, black women, asian women, young women, too young women, raping women, abusing young ugly insecure girls, getting raped, transformation, transsexuals, being dominated, dominating submissive women and so on, almost every "fetish" they have, I have tried in my mind. Some stick and some goes away with time. I don't care and neither should you.
5. If your fantasies still bother you, remember that more you try to stop fantasizing about something, more it turns you on usually. Just accept that it's just how our minds works, nothing about you as a person.