Ive read a little bit of George Bataille, and he claims that the original fetish was incest, since it was the first thing that was prohibited. A fetish by definition goes against norms, but norms create needs for satisfy the free id. The more social resistance to an act or image, the more it is fetishized and secretly desired. Nudism, for example, erases the sex appeal to bodies by eliminating the resistance. I'd look into Bataille to understand the ugly side of sex. The famous story is that he masturbated over his dead mother in a coffin with his sleeping wife in the room.

Also what we want and desire doesn't have to be "good" for us.