Readers are responding to this post in droves. Below are all their best arguments against legal polygamy (with pro arguments coming shortly):

Your readers debate the polygamy objection to gay marriage, but they both miss the actual answer that has been provided by the courts a long time ago – and it makes perfect sense. Bans on polygamy are constitutional because the discrimination is purely numerical and thus applies equally across racial and gender lines, etc. The law says you can only have one spouse, and that law applies to blacks, whites, men, women and, yes, ultimately heterosexuals and homosexuals. It is the same reason it is constitutional to legislate an age when you can marry, an age before you can vote, or the maximum speed that you can drive on a highway. All laws discriminate in some sense. But purely numerical discriminations do not discriminate based on a person’s inherent nature and, thus, are (usually) constitutional. Its also why it is possible (if not necessarily advisable) to criminalize polygamy. Society is free to decide that polygamy is an accepted marital arrangement. Indeed, we already accept serial polygamy (e.g., Newt Gingrich). But constitutional considerations would be implicated if society tried to legislate that only whites or only heterosexuals could be polygamous. At bottom, the polygamy question is a red herring to the gay marriage debate.

Another:

In addition to the excellent response from another reader which you posted, I have to add this: In societies that previously recognized polygamy, it was almost exclusively polygyny and not polyandry; a man could have more than one wife, but no wife could have more than one husband. I’m going to assume that we’re doing away with that scenario on the basis of gender equality alone, but a quick look at the details of what polygamous marriage would look like makes it clear why polygyny (provided legal gender inequality) is actually manageable but generalized polygamy isn’t in most cases.

Let’s do away with genders and just talk about three people, A, B, and C. Person A wants to have a polygamous relationship with B and C. In the US, the primary legal result of marriage is the formation of a single legal household entity that encompasses two people. So, if A and B become one household, and C marries A, are B and C now married too? If not, you have a legal mess on your hands that should be obvious. And it gets worse if C wants to marry D as well, but A and B do not. There is an argument to be made for “group marriage,” where an arbitrary number of people enter into a marriage contract with each other. Let’s also provide that any individual can voluntarily “divorce” him or herself from that married household. I could see a legal basis for this, although my question would be: does this even resemble anything that we would call “marriage” anymore? Is there any way in which the complex group dynamics inherent in human nature don’t split this “marriage” into factions? And for that matter, what really is needed here that isn’t provided by, say, incorporation? Perhaps there’s an argument to be made for arbitrary “adoptive families” that aren’t families at all. For a less explosive example, let’s imagine two unrelated people who come to cohabitate as siblings and not romantically or amorously. In the same way that four co-“married” polyamorous individuals might want hospital visitation rights and inheritance rules, these two people might want some protections without being married. I can see an argument for that, but I can’t see calling it marriage.

Another way to look at it:

The reason for a two-person marriage works much better than three-person marriage is not due to government policy. It is entirely social. Pardon me going all geeky here but this is how I think: Three-unit systems where all equal to each other are inherently more unstable than just two-unit systems. Imagine that the probability of two people having a great interpersonal relationship is x. In a two-unit system, probability of stability is x. But in a three unit system it has to be x to the power of 3, since three relationships have to be great. Note that x is less than 1. So x^3 is much much less than x. A stable society can not function with such a high divorce rate. In ancient societies and in some places even now, polyandry and polygamous marriages are traditional. They work because of special social circumstances and in lot of cases one or more of the persons in the marriage has more weight than the rest and they stay cohesive only because of those special circumstances. Once everybody wants equal weight, things will collapse.

Another points to a variety of complicated scenarios:

What happens if Wife #1 wants a divorce but Wife #2 objects? When the husband dies, are the two women still married to one another? Does the estate get disbursed or do they have to keep on sharing it? The assumption is that if it’s one man and two women, if one of the women dies the remaining man and woman are still married. What do you do in community property states? What happens in the community property state when Wife #2 dies during the middle of the divorce of Wife #1. Does the husband get to keep everything or does the about-to-be-divorced wife get half instead of one-third? If they were divvying up things three ways before she died and she does it three hours before the final decree does the surviving wife have a half interest in the third? What about if she dies three hours after? The husband dies before both wives. Do the kids of Wife #1 get a say in the end-of-life decisions being made about Wife #2?

Another runs through a similar series of situations and concludes:

We do not have the laws in place to support plural marriage. I don’t know for sure, but I suspect that most of the countries that do allow plural marriage allow only one form of plural marriage: a single man and multiple wives. Our constitution will certainly not allow that restriction if we decide to go down that road. We would have to build those laws, and I don’t think we have anyone wise enough to craft laws to cover a fraction of the situations that would develop. People who want some sort of a plural marriage will have to resort to lawyers and contracts to formalize their relationships on a case-by-case basis. I realize that is what people used to say about same sex marriage. The difference between the two situations is that we already have a body of law to govern the marriage of two people.

One more for now:

Please continue to make a clear distinction between gay marriage and polygamy. The best argument for gay marriage is that it harms no one and is good for gay people and their children. No one has managed to come up with even a shred of evidence that gay marriage is harmful to anyone, and not for want of trying. Polygamy, on the other hand, is demonstrably bad for women and children, in ways that go far beyond creating a surplus of unmarried men. An excellent resource on this topic is A Cruel Arithmetic: Inside the Case Against Polygamy, by Craig Jones.

(Photo: the full family of one Joseph F Smith, c 1900, a known polygamist. This picture depicts members of his family, including his sons and daughters, as well as their spouses and children. Via Wiki.)