If you think about it in terms of what is most nasty and unnatural, I think the true order ranks like this:

Most natural and least nasty - Pedophilia. Especially involving any girl already past puberty regardless of her age. If she's 10 years old but can have kids and looks attractive, I think liking such a girl is totally natural (and vice versa for guys).

Semi-natural and fairly nasty - Homosexuality and Lesbianism. Yuck! Although since I'm a guy I don't think Lesbianism is yucky, and many girls probably don't think Homosexuality is yucky either. Hahaha. Actually, there may be ways to argue why one might be naturally yuckier than the other, but I don't want to get into that.