And if males ruled as the only gender, or if females did, then our species would of died out as well. Does that make a specific gender wrong in anyway possible? Nope. Same logic different word my friend, so the point isn't moot.
Homosexuality = being attracted to the same gender
Bisexuality = being attracted to both genders
Heterosexuality = being attracted to the opposite gender
Incest = being attracted to a family member, which isn't even a sexual orientation. It's not relative to any of the aforementioned sexual orientations at all. The comparison is irrelevant my friend :O
And btw, justifiying or unjustifying beastiality, incest, pedophilia has nothing to do with any sexual orientation, so I don't see what you're getting at here.