Princeton professor Robert George attempts to bolster the procreative argument in a recent paper. His argument is that, even though some heterosexual couples can't have children, they are oriented towards that goal through the nature of the act. He makes the analogy to a baseball team: all baseball teams are structured to win baseball games, but some win and others lose. Yet the losers are still baseball teams, and in a similar way non-procreative heterosexual couples are still oriented towards procreation.
Over at Slate.com, Kenji Yoshino responds:
I suspect it will be cold comfort to many infertile opposite-sex couples to hear that while their marriage is still "real," it is a "losing" marriage as opposed to a "winning" one. Ideally, most of them view their marriages as something more than honorable defeats and would despise the contention that they had not fulfilled the central purpose of the institution. Moreover, the article says nothing of straight people who choose not to procreate. It is unclear why they would have "true marriages," as they are not even trying to win.
This argument tells you everything you need to know about the pro-gay marriage side of the debate. The first half of the paragraph hints at the skepticism, made more explicit elsewhere in the piece, that marriage has to do with anything other than the shared love and sexual intimacy of two people. (I'll just say, in passing, that the notion marriage is only about love strikes me as historically, anthropologically and psychologically clueless.) But the second half of the paragraph gets at why, despite my much greater sympathy for Robert George's point of view, I believe Yoshino ultimately has the better of the argument. You cannot argue that marriage is about an orientation towards procreation when a large number of married heterosexuals explicitly reject that belief, not by accident of biology, but by choice. And, what's more important, there are no legal or social repercussions when a married couple chooses not to have children.
However, while Yoshino is right that George's procreative argument does not create a sufficient case for preserving marriage as a heterosexual-only institution, he is wrong that his counter argument makes an effective case for gay marriage. Consider this sentence: "Closely examined, the common-procreation argument denigrates not only same-sex couples but several kinds of married opposite-sex couples." He is speaking about the State, our government, smiling upon certain types of loving relationships and 'denigrating' others. Does our government have any interest, at all, in licensing personal, loving relationships? Especially if no-fault divorce means they can be dissolved any time, or for any reason? Of course not. Gay marriage advocates are arguing for inclusion in an institution that, from a civil point of view, is completely hollowed out. If they were intellectually honest, they'd be arguing for an end to marriage as a legal concept, and its replacement with a system of contracts: we could have a basic civil union that covers things like joint tax filing and hospital visits, and a child-rearing contract that expresses the intention of two people to commit to raising a child (whether conceived by the couple or adopted) to adulthood.
To go back to the question of how you define marriage, it isn't an "either, or" issue, but rather a, "both, and" issue. Marriage is both about love, and procreation, and raising children correctly, and (at least for religious folks) making a commitment to God and Church about how you intend to conduct the rest of your life in partnership with your spouse. But that is very explicitly a religious vision of marriage. In our society, I would argue, the only consistent, valuable definitions of marriage are religious ones.
Our society is deeply influenced by its Christian heritage. However, once that faith ceases to be vital in the public square, that influence is not sustained, which means basic assumptions about our society enshrined in law, like marriage, come under scrutiny. I believe marriage as a civil institution was fundamentally hollowed by no-fault divorce, which strips a sense of duty and commitment out of marriage. That shift in the law was largely embraced by the public, including practicing Christians, who get divorced with basically the same frequency as the public at large. If we wish to have a religiously informed vision of marriage enshrined in civil law, Christians must prove through their actions the superiority of that vision. Until then, the best (and most fair) thing to do is to end civil marriage and return it to the religious sphere where it finds its truest expression.