In most cases, if you grow up eating something, it's normal. If you don't, it's unusual. Sometimes people think things are disgusting when they really mean they're not used to them. I think that explains about 95% of it.
I think there’s an important distinction to be made between being disgusted by the thought of eating escargots and being morally judgemental of the thought of eating horses. That said, it is not a far-fetched idea that moral disgust has its roots in the more visceral feeling of physical disgust, as evinced by the alimentary restrictions imposed by some religions.