I generally prefer to steer clear of social issues here, especially as a mathematical perspective does not often add illumination to them. Discussions of same sex marriage, however, always lead to the question: what harm does it cause? The answer I most often hear is that legalizing marriage between same sex couples will degrade the institution of heterosexual marriage. My attempts to analyze this answer thus far leads only to the creation of spherical horses.
In order to understand the threat to marriage posed by a government action, we first must consider marriage's relation to the government. Libertarians often argue that government should play no role in matters as inherently personal as love and marriage. A natural libertarian position might then be that the government should recognize no marriage - heterosexual or straight. In fact, libertarians often argue that marriage should exist solely as a religious sacrament. I think this argument is attractive on the surface, but fundamentally incorrect.
Every libertarian I have read asserts that government should protect citizens' property rights. Consequently, the government must prevent fraud and help enforce contracts. From my perspective, the most important contract most people enter into is the marriage contract. Unfortunately, the terms and conditions of the contract have become so weak and vague that it is now essentially ceremonial. Question: does this loss of a clear marriage contract fundamentally degrade the institution of marriage? One way to approach this question is to ask what form an optimal marriage contract should take. What sanction does our society impose - what sanction should it impose - on the man who blithely discards his wife of twenty years and three children, replacing her with a younger lady who catches his eye? Should inability to conceive or bear children constitute grounds for dissolution of a marriage? I don't pretend to have answers for such questions and doubt a satisfactory single answer exists in our pluralistic society, but if a couple is be able to agree to the answer before they wed, then why shouldn't the government help enforce that contract like any other? Of course prenuptial agreements exist, but are generally considered distinct from the marriage contract. Perhaps the Catholic and Presbyterian churches should each offer their own approved marriage contract. Perhaps the Sierra Club and National Public Radio could offer their own approved standard marriage contracts too, each with its own list of duties, grounds for dissolution, and penalties for violation. If corporate America can impose noncompete contracts, why can't similar terms be included in a marriage contract: if you leave without grounds, you can't remarry for n years. The possibilities are endless and entertaining to contemplate.
Unfortunately, I do not see what current difficulty such a buffet of personalized choices remedies. I suppose that many engagements would terminate short of marriage when the loving couple is unable to agree on what type of marriage they are entering. When I began toying with the idea of more specific and varied marital contracts, I was thinking of the negative effects of the current very loose divorce laws. However, I'm not sure I would want my spouse to remain with me out of fear of contractual penalties rather than from delight in our mutual companionship. (Of course, someone else may feel differently, in which case the lack of resonance of the idea with my personal situation actually supports the argument for more species of marriage.)
So, I haven't managed to shed any light on any of the questions raised. Classes have begun here. Perhaps I will have to wait until the next class break to actually solve any (nonmathematical) problems.