Marriage: a matter of equality before the law

Here comes another post where I relate an on-going discussion I've been having with a friend. The friend is a self-described conservatarian (part conservative and part libertarian). He struggles with some issues of libertarian ideology such as full drug legalization and same-sex marriage. He is thoughtful in his disagreement, when he has disagreement with my strict-liberty philosophy, and this extends to a careful treatment of the same-sex marriage issues. While he is not yet a supporter of same-sex marriage, he is very tolerant of those who are homosexual, and he is questioning his position on the marriage issues. He is willing to learn.

He brought today a new argument that he had heard recently. For background, this relates to an earlier segment of this debate we've been having where I invoked Mike Munger's rather good argument (I believe it is a very good argument) that the issue is not about some slippery slope to three-way marriage, etc. Today the argument brought was something along the lines of the following (I am paraphrasing and probably butchering as well):

The state should be blind in many respects in the marriage contract: Blind to race, blind to national origin, blind to religion, and blind to sexual preference. But the evolutionarily natural and by far historically predominant state of marriage has been between a man and a woman. If the state begins sanctioning the marriage contract between man and man or woman and woman, then the state is no longer blind to sexual preference. The state is making a judgment about conditions within marriage that it was previously blind to. Therefore, the state should not disrupt the natural and common understanding of marriage (man and woman). Otherwise, why not man-woman-woman? Why not spinster sisters who want to avoid inheritance tax? Etc.

The argument itself is a non sequitur and the additional worry at the end is a red herring. It is a strange twist to say that the state is treating people equally by not allowing some people major advantages it offers others because some don't meet a rather arbitrary condition: heterosexual union. 

As we discussed it further, we seemed to get bogged down in the slippery-slope part where if the state says that being a man and a woman are not essential conditions for marriage, then, according to the argument presented, there is no logical way to draw the line limiting it to two people, etc. The idea is in part an attempt to "corner a libertarian" by making me take a difficult position through reductio ad absurdum. If so, he was barking up the wrong tree. My argument was as follows: 

There may be a logical straight line (pun intended) as well as a liberty-principled reason to support marriage contracts among more than two people, but that is a battle for another day. It is not the current debate, and it doesn't shed light on how we should settle the current debate over same-sex marriage. What's more, many of these hypothetical marriages do not follow logically from allowing same-sex marriage. We can draw lines about what will and what will not be considered a legitimate marriage contract. 

I was searching for an analogy in the law to help make this concrete. At first I thought of liable and how it is different in different jurisdictions and somewhat arbitrary, but with liable we essentially get to a point where a balance is struck. Then I thought patent law might be a better analogy as it is a creation of the state as is the marriage contract (in case it isn't obvious, this entire discussion has nothing to do with how a particular religion defines marriage--it is only about state-recognized contract). But then the best analogy came to mind, and I sent the following email:

Forget the liable analogy. This one is much better, I think, to express my argument against the logic you were laying out this morning: The minimum age we allow people to get married.

This is something that has varied arbitrarily throughout history and varies today across societies. In the US it is usually 18 with the exceptions of Nebraska (19) and Mississippi (21). Most states allow minors to get married with parental or judicial consent generally limiting this group to 16 and 17 year olds. There are also pregnancy exceptions for females below 18 along with some other exceptions in various states.

I would equate same-sex marriage prohibitions with age prohibitions for those 18 or above. So Nebraska and Mississippi become the problem cases. Nebraska and Mississippi might argue that if they are forced to move their restriction down to 18, then why not 17? Why not 14? Etc. That isn't the issue. The issue is if legal, consenting adults can marry. Arguments could be made that those below the arbitrarily-set age of majority, 18, should still be allowed to marry, but that is not the issue at hand. Changing the definition of state-sanctioned marriage to include same-sex couples may weaken the case against three-person or more marriage, but that is not the issue being addressed. The issue is whether the state-sanctioned marriage contract can be rightfully limited to couples that are comprised of one male and one female.

My first-best solution is that the state should have no role in marriage--there shouldn't be a marriage penalty or benefit in tax policy, exchange of assets, etc. My second-best solution is that the state should not discriminate when sanctioning a marriage by considering the genders of the marriage participants. We've come a long way since the Army recruiter's standard question for Winger and Ziskey: "Are either of you homosexuals?" We still have a ways to go.