The story of David Epstein, the Columbia University political scientist and Huffington Post blogger now facing criminal charges of incest, has launched a very interesting discussion. What is fascinating about it, and deeply disturbing, is the inability of some commentators to articulate what is morally wrong about the act of incest. It is almost equally disturbing that a legal argument for a “right” to engage in adult, consensual incest stands on surprisingly firm footing, thanks to precedents the United States Supreme Court has already established in other cases on the “autonomy of the person” under our Constitution.

Professor Epstein, 46, has been charged with third-degree incest for carrying on a sexual relationship over a three-year period with his daughter, now 24. From what little has emerged about the case, there are no charges that the relationship antedated the daughter’s eighteenth birthday, nor has it been alleged that the sexual relations were other than consensual. (The daughter herself has not so far been charged with a crime, however.) So powerful is the contemporary opinion that “consenting adults” may engage, in private, in any acts that commit no “harm” (narrowly understood in almost purely physical terms) to the parties in question or to others, that some observers have merely shrugged indifferently at the Epstein case, while others have striven to find grounds for condemning such incestuous acts but finally confessed their failure to find them.

After briefly describing the facts of the Epstein case, UCLA law professor Eugene Volokh asked, “Should it be illegal, and if so, exactly why?” The comments from his readers were not, in the main, terribly edifying. Volokh’s UCLA colleague Stephen Bainbridge cited the ethicist Leon Kass’s phrase “the wisdom of repugnance,” and said there was “definitely an ick factor” at work in his judgment of the case. But beyond this instinctual support for an ancient taboo, Bainbridge had little else to offer. And such an “ick factor” may be all most people can summon upon learning of this case. The taboo being so ancient, so much a part of “second nature” in people’s moral make-up, it has gone unarticulated for so long that when the need arises to articulate it, we may find ourselves speechless.

William Saletan made perhaps the most successful attempt to articulate a reason for condemning even consensual adult incest. He rejected the oft-cited risk of hereditary birth defects as a reason to prohibit incest, because such a risk is not present in some incestuous relations and is easily obviated in others. And violence and exploitation could not be said to be at work in truly consensual cases of incest between adults. Saletan finally settled, without much further elaboration, on calling incest a “cancer of the family” because it perverts already-existing relationships between family members.

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It does indeed. Saletan might have consulted the analysis offered in C.S. Lewis’s 1960 book The Four Loves had he wished to develop the point. Lewis’s four forms of love are affection (the Greek storgē), friendship (philia), sexual or romantic love (eros), and charity or Christian love (agapē). Here we may stick to the first three—the “natural loves,” Lewis calls them—and observe that they are not so much variations of one thing as different species of love. Each has its own integrity, and is in an important way constitutive of human happiness. Some overlap among or progression through the various loves is possible, of course. Married couples, for instance, may begin as friends, become lovers, and finally find their relationship cemented in bonds of affection, that “humblest love” that as often as not involves a great deal of “taking for granted.”

But while such overlap is appropriate in some instances, in others it is inappropriate—indeed, it can be an outrage to mix loves or for one to intrude upon another. The relations of children to parents, and of siblings to each other, the most basic of familial ties, are intense and lifelong relations of affection, in which great variations on storgē are visible. Such close kinship, grounded in nature or even only in law and custom (as with step-siblings, for instance), is often its own justification and support. Surely many of us have been heard to say something like, “I don’t much like him, but I’m obliged to love him, because he’s my brother.” Introduce the element of eros, however, and affection is not reinforced; it is destroyed, and replaced by something unnatural to the relationship in its proper sense. The human good of parent-child love, or of sibling intimacy, is sacrificed to a misplaced passion that cannot achieve its own rightful end.

Much more could be said on this score, about the natural hierarchies, duties, and trusts that are shattered by incest, even between “consenting adults.” But the recent discussions of this matter reveal how decayed is our moral vocabulary for considering it, how nearly lost is any understanding that our various loves have their natures and purposes, which must be respected if those loves are to conduce to our happiness. Only such decay can account for the failure to grasp that a man cannot be a father to his lover, or a lover to his daughter.

The degradation of our moral sense about these things has been driven by the elevation of eros above all other loves, by the reduction of eros almost entirely to sexual behavior alone, and by a notion of untrammeled freedom to seek sexual satisfaction. In this development, the Supreme Court has played a pivotal destructive role. In its 2003 decision in Lawrence v. Texas, invalidating laws against homosexual sodomy, the Court referred to “an emerging awareness that liberty gives substantial protection to adult persons in deciding how to conduct their private lives in matters pertaining to sex.” As Justice Anthony Kennedy went on to say:

The present case does not involve minors. It does not involve persons who might be injured or coerced or who are situated in relationships where consent might not easily be refused. It does not involve public conduct or prostitution. It does not involve whether the government must give formal recognition to any relationship that homosexual persons seek to enter. The case does involve two adults who, with full and mutual consent from each other, engaged in sexual practices common to a homosexual lifestyle. The petitioners are entitled to respect for their private lives. The State cannot demean their existence or control their destiny by making their private sexual conduct a crime. Their right to liberty under the Due Process Clause gives them the full right to engage in their conduct without intervention of the government.

As I had occasion to write several years ago in the context of another case of incest, if this is sound constitutional reasoning about the “liberty” protected by the due process clause, then it is as sound for the invalidation of incest laws as it is for the invalidation of sodomy laws. By declaring that a law prohibiting a sex act between consenting adults could not even pass the “rational basis” test, the least stringent of the constitutional standards the Court applies, Justice Kennedy in fact invented a kind of super-fundamental right to the sexual satisfactions of one’s choice, so long as one had a willing partner (or partners) past the age of majority. While a federal circuit court and a state supreme court have attempted to divert the reach of the Lawrence precedent from its obvious impact on incest statutes, their arguments unconvincingly deny the plain inferences to be drawn from Justice Kennedy’s reasoning.

Saletan insisted that there is “a rational basis to forbid” incest, even when it is the act of consenting adults—although he seemed also to want to leave his own moral strictures largely unenforced in such cases. The burden of his argument, however, was to distinguish between homosexual relations and incest, giving moral approval to the former while retaining condemnation of the latter. Indeed, as a supporter of same-sex marriage, Saletan argues that while incest is a “cancer” that eats away at the family, homosexuals should be encouraged to marry in order to “form . . . stable famil[ies].”

For our present purposes we can leave aside the question whether same-sex couples can form unions that deserve to be called “marriages,” or whether homosexual relations correspond to the nature or purposes of any of the “natural loves,” as Lewis called them. (On the nature of marriage, see the articles collected here on the debate begun recently by Sherif Girgis, Robert P. George, and Ryan T. Anderson.) What we must notice is that Saletan’s strictures against incest rest on moral arguments of a kind that the Supreme Court has already rejected in the Lawrence case. Above all other considerations, the Court has elevated autonomy, choice, a freedom from being trammeled in one’s private preferences regarding intimate matters of sexual partnering, and even a freedom from being “demeaned” by public disapproval in law or policy of one’s choices in such matters. A majoritarian moral preference for the integrity of the family cannot, in this arena, claim a “rational basis” in the law as against the autonomous choices of free individuals to disregard that integrity if it suits them. There is no such thing, by the inexorable logic of Lawrence, as “the family.” There are only “families,” constituted by the choices of individuals to make them, unmake them, and bend their purposes to their own will.

Whatever the fate of Professor Epstein, his case forces us to choose between alternative courses of reasoning regarding the morality we embody in our law. Do we believe in the “autonomy of the person,” as a constitutionally protected freedom to live as though human relationships were clay in our hands, to be molded as our desires imperiously demand? Or do we believe that sexuality, love, and family are things that constitute us, possessing their own natures and purposes and calling us to answer to them? On our choice between these two understandings, much of our future happiness depends.