A common argument against gay marriage is that marriage is for procreation and gay couples cannot procreate. Let's call it "the procreationist argument." Is it persuasive?
The procreationist argument starts with the indisputable proposition that procreation is indispensable to human survival. It then posits that marriage exists to encourage this indispensable act to occur within a lasting union. The procreationist may concede that marriage has other purposes - for example, providing the married person with a primary caretaker and channeling sexual activity into monogamous commitments. Still, the procreationist maintains, these other purposes serve mainly to help sustain the overarching marital purpose of encouraging procreation and stabilizing family life for the resulting children.
Individual gay persons can procreate, of course, through means such as artificial insemination and surrogacy arrangements. But gay couples, note the procreationists, cannot procreate as a couple. The distinction is important, they say, because parents tend to give better care to biological children than to adopted children. Further, no event helps the durability of a relationship like the birth of the couple's biological child.
According to the procreationist argument, it is the unique procreative capacity of male-female couples that justifies the unique status of marriage itself. It is the one essential attribute of marriage, supplying its historic male-female definition.
But so what? What are the practical consequences of cutting the marriage-procreation connection, as procreationists claim gay marriage would do? I can think of two possible fears. One is that procreation itself would slow down, perhaps below the "replacement rate," the level at which humans must reproduce in order to stay ahead of deaths. This slowdown would imperil the species. The other fear is that, as the connection between marriage and procreation is loosened, procreation may increasingly occur outside of marriage. Both at once could happen, and both would be bad.
What do we make of this argument? If gay marriage would doom human life on earth and/or mean significantly more illegitimate children, it should be resisted no matter how much gay couples need it.
But neither of these consequences seems likely. It's not clear why straight people would stop procreating if gays could marry. The factors driving people to reproduce - the needs for love and to love another, the purported instinct to propagate one's genes, religious obligations - would still exist if Adam and Steve could marry.
It's also not clear why gay marriage would drive more straight couples to reproduce outside marriage. The benefits of marital procreation would still be available to them, after all. The problems of non-marital procreation would still be there to discourage it.
But fortunately we do not have to guess at the probability of these cataclysmic consequences because we already have much experience with severing the link between marriage and procreation.
No couple has ever been required to procreate in order to marry. No couple has ever even been required to be able to procreate in order to marry. Sterile couples and old couples can marry. Couples physically able to procreate but who do not want to procreate can get married.
Many married opposite-sex couples already fit into one of these nonprocreative categories. They are a larger segment of the population by far than gay married couples ever would be. Yet despite their inherent or explicit rejection of the procreative marital duty, humans continue to procreate and marriage continues to be the normative situs for procreation.
The procreationists have two responses to the nonprocreative-couples argument. First, they say laws are made for the general rule, not the exceptions. Most opposite-sex couples can reproduce, but no gay couple can. Second, they argue that the failure to require married couples to procreate is only a concession to the impracticality and intrusiveness of imposing an actual procreation requirement. It is not an abandonment of the procreation principle itself. It would be unthinkable, on privacy grounds alone, to subject couples to fertility tests as a requirement for marriage. We need no such intrusive test to know same-sex couples can't reproduce, the procreationists observe.
The first response is an evasion. Laws often state general rules but provide exceptions where appropriate and just. Gay marriage, like nonprocreative straight marriage, is an appropriate and just exception to the procreationists' rule that marriage exists for procreation.
The second response is equally unavailing. If we were serious about the procreationist project, we could require prospective married couples to sign an affidavit stating they are able to procreate and intend to procreate. If in, say, 10 years they had not procreated we could presume they are either unable or unwilling to do so and could dissolve the marriage as unworthy of the unique institution.
That would be neither impractical nor require an invasive fertility test. That no one has proposed it, or anything like it, suggests we do not take the narrow procreationist vision of marriage very seriously. Marriage is not essentially about procreation because procreation is not essential to any marriage.
Further, this second response suggests that the general rule of procreation must bend to the overriding needs and interests of couples unable or unwilling to live by it. If that exception exists for nonprocreative straight couples, why not for nonprocreative gay couples? If there is an answer to this question, it cannot be found in the procreationist argument.
So the procreationist rule, refined in light of actual lived experience, is this: Nobody is required to procreate in order to marry, except gay couples. It's a rule made to reach a predetermined conclusion, not for good reasons.