After reading the SCOTUS Prop-8 transcript (hilariously condensed by a friend on FB), it seems the anti-same-sex-marriage argument being offered boils down to this:
Opposite-sex couples run the risk of producing children, therefore the state has an interest in enabling these couples to be legally bound, else those children could potentially be a burden on the state. There can be no other reason whatsoever why the state might want to enable a given couple an easy way to bind themselves legally and financially to each other, ergo, there is no reason the state ought to offer such a contract to same-sex couples.
This, as you may note, is slightly different than the argument that marriage is only for producing kids, which is easily shot down by counter-arguments about opposite-sex couples who are infertile or choose not to procreate. No, they’re saying that marriage is there to cover the risk of producing kids, because gosh darnit, those straight people can’t be trusted not to make their crotch droppings a burden on the taxpayer.
But here’s the problem with that: if opposite-sex couples are so scarily at risk of producing welfare-sucking bastards at the slightest provocation, then doesn’t the state have an interest in FORCING opposite-sex couples to marry? Shouldn’t they be jailing straight people who have sex before marriage? Shouldn’t they prohibit divorce for anyone who has kids?*
Of course not. Marriage is voluntary. We understand that people are free to choose it or not as they wish. So, while we can recognize that one of the benefits of state-granted marriage would be ensuring legal and financial child support, we cannot say that that’s the purpose of state-granted marriage.
That being the case, if there are more state interests involved in marriage, then limiting it to couples at risk of procreation makes no sense.
*For the record: It’s not just potential bastard children whose legal status/expensive upkeep would be a consideration under that logic. Back when women were considered property of their husbands, a legal marriage was like having a license for your dog, proving that you had legal responsibility for it. The state’s interest, in such cases, would be the financial upkeep not only of the children born out of wedlock, but the unwed mother, too (because working mothers were more or less unheard of then.) As with feral dogs, a feral unwed mother and her pups would be considered a public nuisance. Ergo: marriage laws ensuring that men kept up their responsibilities as owners of their wives and children.
Thank goodness we no longer see marriage that way, right? Right?