Marriage pre-dates recorded history. You actually believed marriage is defined by Christianity? Are you serious?
There is no scientific evidence or proof of genetic sexuality. None.
Secondly, even if I humored you, then we could call it a disease, a malfunction, the same as many other genetic defects. For it is plainly obvious to our reproductive organs that man and woman should be in union, and not man-man, or woman-woman.
Still, I'd like to see any proof you have, because I have studied it and there isn't any.
sexuality is harmful to your health. It is discouraged by modern medicine. There is a long list of health problems associated with sexuality, mainly in men.
Yes it is harmful to the species, because it blurs gender roles, culture, etc... I am not talking about population replacement.
I am not advocating a sexual witch hunt. What people do in closed doors, we have nothing to do with. I merely don't support the notion of a government legitimizing such a perverse practice, or a culture accepting it.