Bingo. I think this is it right here. So many of the “rules” that God has given us, or that it is reported that God has given us, have a reason. I think that the primary reason against casual sex is to keep people from getting hurt, one way or another. In fact, the first article that I ever wrote that I got paid for (a big $150 back in 1979!) was for U.S. Catholic magazine and was on this very topic.
-Melin