One thing I’ve noticed from both camps in the same sex marriage debate (or any conversation about the nature of marriage) is that our notion of marriage is simply assumed as a given constant. Every debater either approves of or criticizes same sex marriage by trying to force it into an inflexible form as if we had an a priori definition of marriage. Marriage differs widely across cultures and throughout time. The meanings and motivations change as fluidly as language. Gone in the Western world is the need for marriage in the economic engine. Arranged marriages are unheard of outside of isolated communities and marriage has become an almost purely romantic vehicle. If anything, this latter fact has more to do with the rise of same sex marriage than even the gay rights movement itself (for without a change from 18th or even 19th century marriage I think it highly unlikely that the gay rights movement would have been sufficient or even driven to advocate same sex marriage).
It is then disingenuous to put forth the claim that our current ideal of marriage is universal or static. Its reasons are largely arbitrary and the result of a historical and meandering path. Surely it would be politically stupid for same sex marriage supporters to advocate this view, that we can, if we wish, redefine the institution of marriage. Middle America and the median voter wouldn’t have any of it. But the theoretical and legal debate ought to drop the fixation with an a priori definition of marriage.
What benefits accrue to the opponents of same sex marriage stem from foisting this false constraint upon their opposition. They force advocates of same sex marriage (or really any heterodox union - now there’s an ironic choice of words) to fit together two ideals that don’t always fit. Clearly if you choose to define marriage as a joining between one man and one woman then you leave no wiggle room for same sex marriage.
The counter to this is that it seems same sex marriage opponents (perhaps they are advocates of marriage orthodoxy? or marriage homodoxy?) must continually construct explicit and really quite teleological arguments about marriage. That the purpose of marriage is to procreate, the purpose of marriage is to provide a stable place for children to grow up. Yes, most of the purposes of marriage have to do with making babies and raising children.
Note that neither argument in this case obviates polygamy. It’s not a good or purely logical argument to lay claim to historical or extra-cultural (I think I made that up) practices, but polygamy has been used the world over to raise children, and with great success. There are good arguments against allowing polygamy, but I haven’t heard any yet that focus on the institution of marriage and its a priori definition. Rather, they generally focus on why polygamy is ‘bad’, which is to say its effects. But that’s not nice because the loudest argument againsts same sex marriage aren’t based on the effect on individuals but on the definition of marriage.
When the arguments against same sex marriage begin to focus on the [negative] effects of same sex marriage they invariably take one of two tacks, that same sex marriage will push us down the slippery slope to polygamy, incest, and then marriage to animals and the dead; and that same sex marriage is bad for children. Regardless of one’s position on the validity of slippery slope arguments, the slippery slope argument is the more serious of the two, at least in my mind. The argument about children’s welfare can be fairly easily batted away by pointing to the children raised by same sex parents and permanently scarred by the experience (if there are so many how come they’re so damn difficult to count?), the general welfare of children raised by same sex parents compared to average, and even arguments concerning the welfare of children raised by single parents. This is not to say that there are not potentially engaging arguments waiting in this corner, but they’re not the big guns.
The slippery slope argument can take on some interesting forms. If same sex marriage is allowed from a legal standpoint in which individuals should be able to freely enter into contract, then yes, that definition does seem to pave the legal logic for allowing polygamy, ceteris
paribus. After all, if two people can enter into contract to share assets and guardianship, why cannot a third? Granted the addition of a third and beyond lends itself to certain potential complications, however these could be solved much like bankruptcy cases or the garment problem in the Talmud. They are workable challenges, not solid objections.
What of the writ against incestuous marriages? If the logic allowing same sex marriage is that we must not prohibit people from freely entering into this contract, then what is the objection? There are public health objections, that society has a vested interest in preventing inbred offspring, but these objections don’t mesh well with the free contracting argument. Exceptions can always be had of course, but they deteriorate the argument.
It seems to me that same sex marriage can only be contemplated if we’re honest that what we are judging the outcome that we want for our community-at-large, and that as a community there is nothing inherently wrong or dangerous about that. Were marriage considered more closely held as part of the ‘fabric’ of our society or at least acknowledged as that important, we might be actually debating that issue, instead of these side issues of whether one form of marriage is objectively better or more closely satisfies a criterion of liberty. At issue is merely what this society wants to make the institution, and it need not satisfy an existing criteria set.