I think it's not only about having emotional/intellectual connection. For some people, physical cleanliness = moral cleanliness. (And it has nothing to do with any religion.) There's a bunch of things to be disgusted with. What if the person has an STD? What if the person is a killer/thief/unfaithful friend/bad son(daughter)/bad father(mother)? What if he's cheating on his taxes? What if he beats his dog?
If you treat your sexual partner as a body, then having sex is like having lunch or listening to music. However, for someone who sees a personality, the trust is important.