Rational Basis and Constitutional Line Drawing in the Same-Sex Marriage Debate:
I am not an expert in the constitutional debate on same-sex marriage, but I was thinking recently about the relationship between the rational basis test and the need for line-drawing, and how that might impact the constitutional arguments in the same-sex marriage debate. My pondering led me to a tentative argument that I haven't seen directly in the opinions I've read, so I wanted to offer it up and see what folks think. Here's the argument: When the state takes on the task of defining who should receive a government benefit, and that definition requires a great deal of complicated linedrawing, it is presumptively rational for a legislature to draw lines in ways that match traditions or common contemporary practices. As the amount of required linedrawing increases, and it becomes harder to justify one specific line over another, it becomes rational for a legislature to simply mirror the status quo rather than craft a new approach.

  I was thinking about this in the context of the same-sex marriage debate because state recognition of marriage seems to require a lot of linedrawing. It is widely agreed that the state has to impose limits on the number of people who can get married (2? 3? more?), the age of the couples (with or without parental consent), consanguinity (whether cousins can marry), etc. It can be hard to justify the exact lines that get drawn. For example, in many states, couples can get married at 18 without their parents' consent but 16 with their parents' consent. The exact line here seems pretty arbitrary. Why 18 years, and not 17 years and 323 days? Why 16 years if a parent consents, and not 16 years, 4 months, and 19.5 seconds? No matter who draws the lines required to define marriage, some parts of the definition are going to be rather arbitrary.

  My claim — albeit only a very tentative claim, as this isn't my area and I haven't looked closely at the cases — is that the fact that some line needs to be drawn, and the legislature unimaginatively drew it in some relatively traditional way, itself helps provide a rational basis for the legislature's approach. It seems sensible for a state legislature tasked with all the line-drawing of defining marriage to stick with the common answers to the problem. Put another way, deference to preexisting practices in areas that require complicated line-drawing is a sensible default even if we lack a clear argument for why those preexisting practices are normatively preferable to other ways of drawing the lines.

  Again, consider the case of age. Drawing the line at 16 instead of 16 years, 4 months, and 19.5 seconds isn't rational because we think the age of 16 is actually better. Rather, it's rational because some line is needed and there is a tradition of using integer years since birth as a yardstick for entitlement to government benefits that we rationally confer based on age. (It might also be rational because it is easier to calculate, but I think the point stands.)

  In the context of the same-sex marriage debate, then, it seems to me that the need to draw lines and the traditional limitation of marriage to opposing sex couples itself helps provide a rational basis for using the traditional definition of marriage as between a man and a woman. A legislature trying to answer the many questions and line-drawing exercises required by any definition of marriage could reasonably adopt the traditional way of doing things rather than have to justify new lines. Adopting the traditional definition in the face of the significant uncertainty of the best way to draw all the lines required by state recognition of marriage becomes a reasonable means -- perhaps not the best means, but a reasonable means -- of achieving the legitimate state interest of all the traditional benefits of the institution of marriage.

  Two caveats apply. First, this argument is only in play if the constitutional standard is mere rational basis scrutiny. If you believe that heightened scrutiny should apply, I don't think this argument is relevant. Second, I should emphasize that this is a constitutional argument, not a policy argument. From a standpoint of policy, I am in favor of laws permitting same-sex marriage. The constitutional question is not whether I favor the law, however, but only whether such a definition of marriage is a reasonable means of achieving a legitimate government interest.

  Anyway, that's my tentative argument. I'm interested in your responses, especially if you disagree.