Our views about marriage are multifaceted, and the primary facets are two. On one hand, we think marriage has something to do with reproduction and its consequences; on the other, we think it has something to do with the experience of two people who are in love.
Opponents of same-sex marriage think the law should concern itself only with the first facet and must not define marriage other than in terms of its orientation toward procreation. I think the law has a legitimate interest in both facets and can reasonably address the public-policy considerations related to each.
I will call that position “traditionalist” according to which legal recognition of marriage should be restricted to unions of a man and a woman. The traditionalist holds that there is a pre-legal fact as to what marriage is, namely “comprehensive union” of two persons, and that only a “reproductive unit” can be a comprehensive union, although marriage qua comprehensive union is intrinsically valuable whether or not a couple reproduce. I use terms of Sherif Girgis and Robert P. George, both of Princeton, and Ryan T. Anderson, editor of Public Discourse, in their Harvard Journal of Law and Public Policyarticle “What Is Marriage?” They say that to exist as a person involves a bodily dimension as well as cognitive, volitional, emotional, etc. ones, and that any union which is not bodily will by that omission fail to be comprehensive. What unites the organs of a single person’s body is their coordination toward achieving the biological purposes of the organism as a whole. When it comes to one such purpose — reproduction — the organism is naturally incomplete. Only a man and a woman, and not two persons of the same sex, are able to join their bodies in such a way as to achieve this purpose.
Coitus achieves bodily union, traditionalists say, whether or not the couple intend to reproduce or are capable of reproduction. It is because any instance of coitus belongs to the kind of act that is reproductively oriented that the relationships of infertile couples, but not those of same-sex couples, are potentially marital. Traditionalists also say that it would be practically difficult and/or wrongly intrusive for the state to assure itself that a couple are fertile before marrying them.
Why does the law concern itself with marriage at all? A conservative might feel special force in the question, for a conservative wants the state at a large remove from his life. The answer, as the editors of National Review have put it, is that the legal institution of marriage exists “to solve a problem that arises from sex between men and women but not from sex between partners of the same gender: what to do about its generativity.” Sociology demonstrates that children are better off when raised by their two biological parents than when raised by single, cohabiting, or stepparents, although no methodologically rigorous research compares the former condition with that of being raised by two parents of the same sex. The norms of marriage — monogamy, fidelity, and thereby permanence — help bring it about that as many children as possible grow up with their biological parents. Legally recognizing marriage puts the force of the law behind the norms. It once did so by criminalizing behavior at odds with them and imposing a barrier to separation in the form of divorce. Today it is more permissive of liberty (libertinism?) and divorce, but its very existence reinforces the norms by focusing the public mind on the connection between sex, procreation, and marriage.
If the law called same-sex unions “marriages,” it would obscure that connection and make the norms seem to have no purpose. Additionally, gay couples are statistically more likely to flout the norms than heterosexual ones, so we must worry that their inclusion would by example encourage rebellion (though neither Girgis et al. nor the NR editors rest their case on this latter argument).
Traditionalists see no injustice in excluding same-sex couples from the institution because to discriminate is to treat like cases differently, and same-sex couples, not being reproductive units, are unlike heterosexual ones. Same-sex couples are also mostly free to make whatever legal arrangements they wish concerning property, inheritance, medical care, etc. It is a hassle to make such arrangements piecemeal, and a same-sex couple is at greater risk not to have made them before times when they would be important, but some traditionalists meet this objection by endorsing civil unions.
I will call that position “revisionist” according to which the law should be willing to marry same-sex couples. The form of revisionism I will present agrees with traditionalism that there are pre-legal facts about what marriage is, but differs in its account of what the facts are and why the law should care about them.