Which is getting back to the religious crap of "sex is only for reproduction, between a married couple". Yes sex can result in reproduction, but I think making that its primary purpose misses the point. We experience a desire to fuck, separate from our desire to reproduce. They're two different things that are only related in a tiny minority of circumstances. Classifying someone's sexuality by its possible reproductive outcome is like classifying their tongues by the ability to curl into a tube: kinda valid, but not that useful.