This morning I was listening to yesterday's segment of Tell Me More on NPR on whether same-sex marriage would legally require allowing multiple marriage. The correct answer, of course, depends on which arguments are used for same-sex marriage, because some of them do require allowing multiple marriage, and some of them don't. If you argue that people should be able to marry whoever they want, as long as it's consensual, then there seems to be nothing to rule out multiple partners at once. If you argue that it's a violation of gay people's rights to prevent them from marrying someone they have an orientation toward when straight people get to marry someone they have an orientation toward, that sort of argument doesn't easily translate to marrying more than one person at a time. You're trying to give equal rights to everyone, and the rights you give might restrict it to one partner per person.
Jonathan Rauch was one of the guests on that segment. His overall argument is that same-sex marriage doesn't threaten traditional marriage but adds to it, since it doesn't actually detract from anyone's traditional marriage. It doesn't subtract marriages but adds them, and we need more marriage, so same-sex marriage can only help. His argument isn't sensitive at all to the lines of thought involving natural purposes, as traditionally marriage has been thought of, so it doesn't touch some of the more common arguments against same-sex marriage. But his dismissal of that kind of argument isn't new. He's written much of the subject and standardly argues that way. Here's he's assuming there's no such argument without actually arguing against it, but I think he has spent time arguing against it elsewhere.
But here's an interesting argument that's new to me:
Remember, fundamentally what I tell people is when straights get the right to marry three people or their dog or a toaster, gay people should have that too. But until then, that's not what we're talking about. We just want to be able to marry someone instead of no one.
On one level, this argument is silly. There's no ban on gay people marrying anyone, and there's no ban on them marrying anyone that other people of their sex can marry. In that respect, they have the same rights as straight people of their sex in a location where there's no legally-recognized same-sex marriage. What they don't have is the rights that people of the opposite sex have, namely to marry someone of their sex. So you can't argue for same-sex marriage by saying that a gay man doesn't have the same right I have to marry a man. As a heterosexual man, I don't have that right either. A gay man has the same rights I do with respect to the class of people we can marry. (Well, technically, that's true only if he's married. If he's not, then he has a much larger group he can marry, since it's above zero. So, to be more careful, an unmarried gay man can marry anyone of the same class of people that an unmarried straight man can marry.)
But what Rauch really means is that a gay person can't marry anyone in the class of people they'd want to marry, while straight people can. He's arguing for that right for gay people too. Given that he wouldn't want to marry a woman, giving him that right doesn't help him with the actual goals he might have for himself in marriage, which would be to be married to a man.
This argument, interestingly, would not help with interracial-marriage bans. Rauch's resistance to multiple marriages from a same-sex marriage perspective is that only allowing some options is enough. It's not violating his rights if you prevent him from marrying dogs, toasters, and so on, as long as you're doing that with straight people too. By the same reasoning, though, it's not violating his rights to prevent him from marrying black people, as long as you're doing that with straight people too. He's allowed for the compatibility of same-sex marriage with opposing multiple marriage on one level, but you have to look at all the moral positions and arguments he endorses to see if his view really allows for it. You have to bring in other moral premises to see why interracial-marriage bans are wrong, for example, because his argument doesn't get you that far. The question is whether other arguments he'd agree with can supply the necessary resources to argue against interracial-marriage bans. But then there's also the possibility that moral arguments he gives for same-sex marriage would also provide resources to argue against banning multiple marriages.
So his argument here doesn't show that he can resist multiple marriage consistently. It shows that someone could support same-sex marriage and reject multiple marriage. Whether he could depends entirely on the arguments he uses for same-sex marriage, some of which do require recognizing multiple marriage and some of which don't. I do think quite a lot of them do, and many of those are presented by people who want to avoid legal recognition of multiple marriage. This issue will eventually reach the courts, and it's one that those who deal in the business of moral and legal arguments should think about more carefully.