As we watch the final collapse of the political opposition to the idea of something like "gay marriage," it might be worth reviewing why the idea seems so difficult to oppose on rational grounds. The reason is that we have failed to recall what marriage is for, and why society has a duty to support it.
In Aristotle's
Nicomachean Ethics, Book VIII, Aristotle talks about a kind of ethical society based on friendship. He envisions an arrangement that looks very much like this thing we have started to call "gay marriage" -- it is an ideally-permanent union of two (or more, but usually only two) people, for the purpose of each other's happiness (happiness here is
eudaimonia, the rational pursuit of virtue), involving all property held in common. He assumes the two people will usually be men.
There's nothing wrong with such a union. In fact, if it is done on Aristotle's grounds, it's quite right -- and need not include any sort of sexual element, homo- or otherwise. Much of our inability to formulate a rational rejection of 'gay marriage' comes from the fact that the form they are asking for is unobjectionable.
What is objectionable is the error of conflating it with matrimony, which is a wholly different institution with a wholly different purpose. The purpose of the ethical society is the happiness of the two people who create it. The purpose of matrimony is not principally about the two people who form it at all, and is certainly not about their
happiness. Matrimony is principally about the creation of a blood tie between two families, so as to provide resources that sustain and educate the next generation.
The reason society has a duty to support marriage, and the families it forms, is that society depends on its function. Society will die if a certain number of men and women don't form marriage-based families, creating and educating their young to assume social roles as adults. This traditional recognition is why marriage involves all the attendant forms of support that it does: for example, the idea that your spouse and children ought to have access to your medical plans at work, or the idea that society owes a duty to support a widow(er) and/or orphans of a working spouse.
We lost the ball when we stopped treating marriage itself according to its own norms, and allowed it to evolve in to a sort-of ethical society of friendship. We can see this in the kind of writing that people do about marriages: you should marry if it will "make you happy," the most important person in the marriage is your spouse (whose happiness should be valued above the children, because after all the children will grow up and leave someday), divorce should be available whenever a couple would be happier divorced than married. All of this makes sense if what we are calling "marriage" isn't traditional marriage at all, but a kind of ethical society based on friendship.
It's easy to see how the error was made. Even Aristotle himself talks about cases in which a man is friends with his wife. The unity of property has already occurred in marriage, and the bond is permanent, so why not try to be friends too? There is no good reason why not, and indeed many excellent reasons to do so. The only concern is that you don't forget that the marriage has a different purpose than the friendship, so that the duties arising from marriage persist even if (for whatever reason) your friendship ends. Especially in cases when the blood union of the marriage has been realized in children, the duty to support the unity of your families persists even if you come to hate each other. It can only be rightly broken in cases of severe violation of the duties of the union by one spouse -- traditionally adultery and physical abuse. Even then, the duties survive the dissolution of the union: this is what lies behind our legal institutions of alimony and child support. The violator must continue to answer to his or her duties, even if the spouse can no longer be rightly asked to live with such a person.
Ethical societies need to be considered separately, and if
'the ship has sailed' on treating them differently from marriages, then we must rebuild marriage and family under another name. We must then also strip what we are now calling "marriage" of its social support, because it is unjust for society to be asked to support a union that is only about the happiness of the two people united. There is nothing wrong, and much right, with such a union: but society has no interest in it. You have no right to demand of your employer that he should support your
friend. You have no right to demand it of your fellow citizens as tax-payers.
It would be better, of course, if we can make the old distinction stick. I wonder if we can. American society has grown selfish and self-centered, and I wonder how many Americans are still capable of accepting any permanent duty to anything besides their own happiness. If that ship has sailed, none of this current debate will matter. We who survive will be rebuilding the old order from the ashes.