it's not the actual act that they disdain so much, it's the circumstances that come along with it. The chaos, problems with intimacy, probable abuse/abandonment childhood they had, and their poor boundaries represent what poor parents they will be. Kid's need stability and parents with strong boundaries. Drew and adam always said that if you don't have kids, enjoy..but once you have child, all of your energy and actions need to go to creating a stable environment for that child.
Dr. Drew seems like a quack here. Just because he is a doctor doesn't mean he gets to dictate to everyone what kind of sexuality is healthy, and how a relationship should be defined.
Yeah, I liked this show but I used to think the same thing. He is an MD, not a relationship expert. He would make up his mind on a situation and pretty much wouldn't even consider the thought that two adults could willingly do things with one another.