The third mechanism that I posit as likely to undermine marriage should the definition be changed to include same-sex couples speaks to the core justification of public recognition and government encouragement of the institution.
As I argue in terms of the first mechanism, if the state’s irreducible interest in encouraging marriage is to foster mutual care, with its various benefits, then subsequent borders around the definition will not withstand assertions of individual freedom to choose the other person (or the other people). In terms of the second mechanism, I argue that one of those borders is the presumption of sexual intimacy; people with non-sexual relationships would rightly have a claim to benefits that are intended to encourage stable interdependence.
With or without sexual intimacy, if marriage is primarily about the spouses’ watching over each other, then doing the hard work to keep a marriage together depends more on the man’s (or woman’s) desire to care for a particular woman (or man) than on a personal interest in watching over any children whom they’ve created. There was a time when a man who impregnated a woman was expected to marry her as a matter of course. Now, it’s hardly expected that parents should compromise their own emotional impulses so that children born within their marriages can be raised within them, as well. Same-sex marriage would etch this corrosive definition of marriage unreformably into the law.
It is at least plausible to suggest that the reality of same-sex marriages would not affect current marriages between spouses intent on staying together. The obvious observation, however, is that such couples don’t need public encouragement in the first place. As with any cultural institution, marriage involves a broad social transaction of investment and benefit: Healthy, advantaged couples model their relationships toward an ideal of marriage for the benefit of those who incline toward the wrong track.
Sterile couples (as actually rare as they are) and the elderly do not disturb the simple message of the investment, because it is clear, on a fundamental level, that an intimate relationship exclusively between a man and a woman is about that which a man and woman can uniquely do together: create children who are the merger of their two genetic and ancestral lines, their two selves. In ordinary dealings with married couples, one cannot tell the parents from the non-parents. Among the latter, one cannot tell the sterile from the attempting from the expectant from the regretful. It is simply known that men and women who are intimate with each other get married, and with the vast majority of marriages’ involving procreation, the message is clear.
In part through the law (from no-fault divorce to on-demand abortion), modern culture has made a shameful effort to distort clarity about familial ideals and healthy social behavior. And as one might have expected, that legacy has most harmed those in most need of guidance and encouragement toward good decisions: the poor, the oppressed, and the wayward. If is justifiable to fret about polygamy’s ability to create a permanent male underclass, it must be more so to worry about a permanent underclass of bastard children and their irresponsible parents.
In part because it ultimately provides cost savings from social programs serving that underclass, the government’s role in the cultural transaction that is the institution of marriage is to acknowledge it and to offer some incentive to fulfill its objective. Culture is fluid, and it would be contrary to the grand idea of our nation to deny citizens the right to work to change it, but government recognition of same-sex marriage would not only open the way for its diminution by dissipation, it would provide the baseline definition by which the culture must operate and would thereby ensure that it fails to operate.