It is remarkable that the idea of same-sex marriage has gained ground so rapidly. Those most quick to accept the idea have been elite liberals, with ordinary Americans lagging behind but becoming more accepting of the idea. In the thick of the struggle over the law and politics of marriage, we can easily forget how novel is the idea of two men or two women marrying each other.

This fact came home to me when I participated in a forum on the subject at Princeton University last spring. Present in the room were two lions of the liberal academy, each past the “threescore years and ten” of which the Psalmist speaks, each a distinguished scholar with many publications to his credit, each known for his devotion to liberal causes. Both gentlemen expressed the opinion that the cause of same-sex marriage was obviously just, that opponents of the cause were obviously reactionary and benighted, and that this was plainly the new civil rights struggle of our time.

Yet it struck me that if denying same-sex couples the “right to marry” was such an obvious and gross injustice as to merit such energetic claims today, why had it never occurred to either of these august scholars decades ago, at the beginning or the middle of their careers? In the books of proud advocacy each had published, say, twenty or thirty years ago, there was not the slightest hint that American public life was disfigured by this particular injustice.

Redefining marriage to include same-sex relationships simply didn’t occur to them, because it didn’t occur to anyone. Yet that day they espoused that view with the fervor of men who had always thought so, and for whom it was unthinkable to believe otherwise. If they reflected on this change in their own thinking, would they conclude that their reasoning powers had been deficient years ago, or their moral sympathies inadequate?

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It is, of course, possible for people to evolve in their thinking, and to come to views that weren’t on their radar in earlier days. But this seems to be a special case, not accounted for by the emergence of a genuinely new issue, nor by new knowledge, nor by a change of heart or of mind about something basic. The scholars of whom I speak, for instance, have been liberal in their attitudes toward homosexuality for many decades. One could well believe that mistreatment of homosexuals was wrong, without believing it was even possible for two persons of the same sex to marry.

If we compare the issue of same-sex marriage to an issue with which it is often equated, that of interracial marriage, we find that it stands out as unusual yet again. Like slavery itself, the now-discredited ban on interracial marriage was never without critics who complained of its injustice. Only racists thought such a ban was just, and Americans were not universally racist.

By contrast, no advocates of justice in human history, prior to the modern sexual revolution in the West, ever thought of same-sex marriage, whatever their views on society’s treatment of homosexual persons. This historical reality brings us to Michael J. Klarman’s new book, From the Closet to the Altar: Courts, Backlash, and the Struggle for Same-Sex Marriage. Klarman, a Harvard law professor whose very large book on the struggle for African-American civil rights won the prestigious Bancroft prize in history, has written a much shorter book this time around because all the history he relates is so very recent. Every significant element of the story has occurred in just the last twenty years. And the overwhelming impression one gets, in the pages of From the Closet to the Altar, is of social change taking place at dizzying speed, with very little thought about where we are going.

Strictly a legal-political history in its first eight chapters, Klarman’s book is a thorough and instructive tour of the last few decades, but only on a very narrow subject. The author’s tight focus on the marriage issue makes the book unsuitable as a history of American sexual attitudes and mores, of homosexuality generally, or of other “gay rights” issues; all these subjects tangentially appear only in connection with the marriage question. The spotlight is on activists, lawyers, judges, politicians, and public officials as they battle over whether marriage will be redefined to include same-sex relationships; in the background are voters and the general public as the terrain of the contest among elites.

But here is perhaps the useful reminder provided by Klarman’s book. Not only did no one ever believe, before the last few decades, that justice required us to redefine marriage as the solution to some problem. Among gays and lesbians themselves, it remained highly contentious, until still more recently, whether marriage was even something they wanted. They universally desired better treatment from the larger society, but it was by no means universal among them to desire marriage as the mark of that better treatment. And it was not just a question of whether they wanted to press for marriage now or later, as a tactical matter; it was an open question whether they wanted it at all. In the memory of any of us of middle age who have known gays and lesbians all our lives, we quite vividly recall the commonly expressed view among them, not long ago, that marriage was “for straights,” or “for breeders,” in the patois of the gay subculture.

Of this we should pause and take stock for a moment. The consensus among gays and lesbians today (with very few dissenters) is that they do indeed desire the right of civil marriage. But why do they want it? The question is seldom asked. They so plainly desire it so very much that it seems rude to ask.

Well, why have men and women throughout the ages wanted to marry—to unite with each other in a private relation that is publicly recognized, honored, and commonly sanctified? The answer may be found in another recent book, by Sherif Girgis, Ryan T. Anderson, and Robert P. George, titled What Is Marriage? Man and Woman: A Defense. Sexual attraction and romantic love may prompt a couple’s desire to be together, but they marry in order to make something new that honors and ennobles that attraction and love: the nucleus of a family, in a comprehensive relation of husband and wife that points toward the future, with an openness toward making that future through procreation.

We know that marriage can take place without procreation, and most assuredly procreation can take place without marriage. But as a public institution founded on private relations, marriage would not exist were it not for the offspring that regularly result from marital acts. And so, ask the question again: why do (typically young) men and women get married? What purpose are they pursuing? In the paradigm case, the answer is: to start a family in the way all families are made possible in nature, by sexual intercourse and childbearing.

Same-sex couples can and do raise children, but in no case can a child be the offspring of both partners. The family-with-children headed by a same-sex couple, then, is by definition an exceptional case, and cannot ever be the paradigm case of a marriage-based family. In this it resembles opposite-sex couples with stepchildren or adopted children, but only superficially. The difference that still remains is that these opposite-sex couples can provide their children with both a mother and a father, which same-sex couples cannot do. Whether that is a difference that makes a difference is a fitting question, not one to be banished as invidiously discriminating before it is asked.

Where the “conjugal view” of marriage is concerned (as What Is Marriage? calls it), as opposed to the “revisionist view,” something both natural and necessary is pursued. Uniting sexually complementary persons so that new life is brought into the world, and children are provided with mothers and fathers (and this by adoption or stepparenting or the like where “nature” fails), is what marriage has always been about at its core. And it is in order to foster this union and its fruits that marriage is recognized and protected by the laws.

In the revisionist view, marriage comes to be about something else. Throughout Klarman’s book one encounters this fact, though the author, whose prejudices are entirely in favor of this change, makes no effort to present it. For same-sex marriage advocates, marriage is about material benefits (of financial advantage, inheritance rights, control of medical care, etc.), or it is about social status and recognition (the attainment of equality under the law for a relationship hitherto left out of its ambit), or it is about a liberationist ideological project (the normalization and acceptance of homosexuality by the “heteronormative” larger society), or it is about some “transgressive” project (to transform our understanding of marriage because its traditional norms are thought to be unjust, or part of a larger fabric of injustice).

How strange this all looks from the standpoint of the tradition these advocates presumably seek to join. Men and women too might marry for some of these reasons (e.g., for material advantage or status), but they are not why marriage exists, and we are inclined to think ill of couples whose reasons for marriage do not go to the core of its purpose and nature. A change to the definition of marriage that eliminates, among its essential features, the purpose for which it came into being in the first place, is quite a step to undertake.

Throughout From the Closet, we find leading figures in the fight for same-sex marriage trying to divert the attention of voters, legislators, and judges away from the very unorthodox nature of the claim they are making on marriage as an institution. Again and again they are portrayed as pressing on accepted precepts of equality—the condemnation of “discrimination,” the application of “rigorous scrutiny” by judges to claims on behalf of tradition, and so on—as though the thing they so ardently desire were simply an extension of marital norms on which all agree.

Yet this is an astounding case of misdirection. The truth is that they wish to redefine a foundation stone of human society in such a way that it will no longer bear the weight we put on it. As others have observed, redefining marriage to include same-sex relationships completes the separation of marriage from its true nature, already begun by modern divorce law and other social changes, by making it about adult desires rather than the formation of families and the welfare of children.

Klarman turns, in the final three chapters of his book, to the correlation of forces that, in his view, will “inevitably” result in the establishment of same-sex marriage in the whole United States, probably as a result of a Supreme Court ruling in the near future. Here the most striking thing, coming from the pen of a law professor and constitutional historian, is how little interest he takes in the legal arguments and their persuasive connection to constitutional principles. Klarman seems to regard the Supreme Court justices as life-tenured Solons, lawgivers for the nation who act on their own moral convictions, and a rough sense of public opinion, rather than on legal principles discernibly present in the supreme law of the land to which the people have consented.

It is best not to be too confident of the success of a movement that has existed for so short a time, is so unsure of its arguments, and is so heavily reliant on a cynical view of constitutional government. With two cases on the Supreme Court’s docket, we will find out very soon how well moral and legal incoherence hold up, in the court of law and the court of public opinion.