This crappy argument again? SIGH! Humans are not mere pieces of equipment, jackass. You're just objectifying humans this way. We are allowed to choose who to partner up with for life, and there's not a damn thing anyone can do about it.
Besides, you know, as opposed to seat belts, marriage isn't responsible for anybody else's safety. So it doesn't matter if the "ends" are compatible with each other or not.
Unless, of course, you are implying that the only purpose of marriage is to make babies? So does that mean that infertile or disfigured people shouldn't get married? What a hateful, selfish piece of shit you are.
EDIT: See? Swede already said it.
Also, a woman can get pregnant without having to have sex with a man, through artificial means. So your argument's even more invalid.
Seriously, it's old-fashioned assholes like this with their "sanctity of marriage" crap that makes me think marriage is a mere lawful contract at best and an outdated barbaric ritual at worst. Even if it's not fully in my nature, I'd rather be in a (marriage less) polyamorous relationship with several women and have children with them like that, than marry one just to be a baby factory. Just to spite bastards like this.