The audience in New Hampshire let Santorum get away with the silly argument that goes "if we allow gay marriage we'll have to allow polygamous marriage." Listen to the video. Santorum says "Are we saying that everyone should have the right to marry?" Audience: "Yes!" Santorum: "So anybody can marry several people?" Audience erupts. Santorum: "So if you're not happy unless you're married to five other people, is that OK?" Santorum keeps pressing the point: "If it makes three people happy to get married, what makes that wrong?" The audience says it's irrelevant. Santorum says we should employ reason: "Reason says that if you think it's OK for two, then you have to differentiate with me why it's not OK for three." The audience doesn't rise to the occasion, but instead boos him as he leaves the lectern.
Liberals need to be better prepared for this sort of tussle. The answer to the opening question--"Are we saying that everyone should have the right to marry?"--should be "No". People can have whatever relationships they want, but legal marriage is an institution societies use to honor and incentivize relationships that are valuable to the society. Two-way marriage, whether straight or gay, is socially valuable in a way that polygamy is not. Here's the differentiation Santorum was looking for:
In a two-way marriage, both people involved are desirous of the marriage. The marriage is a kind of contract or exchange--I'll do certain things for you if you'll do them for me. There are benefits to this for the society as a whole. People need government support less when they have a long-term, intimate partner.
In polygamy, as it's actually practiced in the real world, three or more people don't suddenly decide to get married. Rather there's a first marriage, and then more wives are added to the marriage (yes, wives--polyandry is extremely rare). The first marriage is mutual in the usual way, but then more wives are added to the marriage, contrary to the preferences of the first (second, etc) wife. (If you think first wives welcome additional wives, dream on!)
It stands to reason that the additional wives put the welfare of older wives at risk. And yes, of course the new wives do tend to get younger and younger. Certainly, there's nothing consensual and mutual about the relationship created between the wives--they didn't desire a co-wife. This non-mutuality does not pertain to gay marriage at all. Gay marriage is just as mutual as straight marriage.
Next differentiation: for each additional wife a man takes, some other man is deprived of the opportunity to marry. This is bad on a personal level for bachelors, but also bad on a social level. Bachelors have poorer health, but they also commit more crime. The problem of the bachelors isn't a fantasy--it's a reality in countries like India and China where gendercide is commonly practiced. In southern Utah, where Mormons practice polygamy, bachelors wind up having to leave the community. One man's gain is another man's loss.
Same-sex marriage doesn't have that drawback. When gay people marry each other, there aren't more bachelors and bachelorettes as a result, because whether they marry or not, gay people are going to be in same sex relationships. Only polygamy gives the benefit of marriage to some people at the direct cost of taking the benefit away from others.
Next differentiation: men with lots of wives have lots of children. With each additional wife, the father-to-offspring ratio becomes less favorable. And it's just not true that a man can nurture and provide for two children as well as he can for 12 or for 24. Gay marriage does nothing to worsen the ratio between parents and offspring, but polygamy does.
There are lots of reasons to honor and incentivize only two-way marriages. So it's just not true that, in all consistency, we must legalize polygamy if we legalize same-sex marriage. Polygamy is different in lots of ways, and you just have to think about it a bit to see why.
Another argument conservatives make is that if gay marriage is legalized, we'll have to let people marry their dogs. Seriously, people say that, as if there's no conceivable reason why a society might honor and incentivize marriage between two men or two women, but not between a man and his golden retriever. Help!
