Of all of the arguments against same-sex marriage that I have encountered, the most ridiculous has got to be the argument that if we accept same-sex marriage, we have to accept polygamy as well. The argument is absurd for a number of reasons. Let’s focus on two of those reasons.
The first reason the argument is absurd is that it relies on the slippery slope, which as we all ought to know, is a conditional fallacy. When you run into the slippery slope, it is really best to do a 180 degree turn and run the other way as fast as humanly possible, but unfortunately, a host of opponents of same-sex marriage have decided instead to embrace the fallacy and put it forth as an actual argument, hoping against hope that no one notices that doing so is a bad idea. Just because we have decided that same-sex marriage is a constitutional right–and just because many people have concluded (rightly, in my view) that it is good public policy to support and implement laws allowing same-sex marriage–that does not mean that we are also obliged to conclude that implementing laws allowing polygamy constitutes good public policy. We can draw a line between the two, and any halfway intelligent society would do so, without sacrificing its ability to sleep comfortably at night, secure in the knowledge that it has remained intellectually consistent and rigorous in doing so.
The second reason flows neatly from the first: Polygamy would lead to terrible public policy outcomes. Jonathan Rauch explains:
I am a gay marriage advocate. So why do I spend so much of my time arguing about polygamy? Opposing the legalization of plural marriage should not be my burden, because gay marriage and polygamy are opposites, not equivalents. By allowing high-status men to hoard wives at the expense of lower-status men, polygamy withdraws the opportunity to marry from people who now have it; same-sex marriage, by contrast, extends the opportunity to marry to people who now lack it. One of these things, as they say on Sesame Street, is not like the other
[. . .]
Unlike gay marriage, polygamy is not a new idea. It’s a standard form of marriage, dating back, of course, to Biblical times and before, and anthropologists say that 85 percent of human societies have permitted it. This means we know a thing or two about it.
Here’s the problem with it: when a high-status man takes two wives (and one man taking many wives, or polygyny, is almost invariably the real-world pattern), a lower-status man gets no wife. If the high-status man takes three wives, two lower-status men get no wives. And so on.
This competitive, zero-sum dynamic sets off a competition among high-status men to hoard marriage opportunities, which leaves lower-status men out in the cold. Those men, denied access to life’s most stabilizing and civilizing institution, are unfairly disadvantaged and often turn to behaviors like crime and violence. The situation is not good for women, either, because it places them in competition with other wives and can reduce them all to satellites of the man.
I’m not just making this up. There’s an extensive literature on polygamy.
Here’s a 2012 study, for example, that discovered “significantly higher levels of rape, kidnapping, murder, assault robbery and fraud in polygynous cultures.” According to the research, “monogamy’s main cultural evolutionary advantage over polygyny is the more egalitarian distribution of women, which reduces male competition and social problems.”
The study found that monogamous marriage “results in significant improvements in child welfare, including lower rates of child neglect, abuse, accidental death, homicide and intra-household conflict.” And: “by shifting male efforts from seeking wives to paternal investment, institutionalized monogamy increases long-term planning, economic productivity, savings and child investment.”
There’s more, but you get the idea.
In this article, I noted other research suggesting that societies become inherently unstable when effective sex ratios reach something like 120 males to 100 females, such that a sixth of men are surplus commodities in the marriage market. That’s not a big number: “The United States as a whole would reach that ratio if, for example, 5 percent of men took two wives, 3 percent took three wives, and 2 percent took four wives—numbers that are quite imaginable, if polygamy were legal for a while.”
By abolishing polygamy as a legal form of marriage, western societies took a step without which modern liberal democracy and egalitarian social structures might have been impossible: they democratized the opportunity to marry.
Read the whole thing. Rauch neatly and expertly demolishes the notion that a society that has accepted same-sex marriage also needs to accept polygamy. I am not naïve enough to believe that we have heard the last of this nonsensical argument, but no fair-minded person can possibly believe that we ought to take it seriously.