There are certain questions now pressed upon us that previous generations would never believe could be asked. One of these is thrust upon us by events in New York City, where a well-known Ivy League professor has been arrested for the crime of incest. What makes the question urgent is not so much the arrest, but the controversy surrounding it.

David Epstein is a professor of political science at Columbia University, where his wife also teaches. He previously taught on the faculties of Harvard and Stanford. Last week, he was arraigned before a judge in Manhattan, charged with a single count of felony incest. According to authorities, Professor Epstein was for several years involved in a sexual relationship with his adult daughter, now age 24.

Though the story was ignored by much of the mainstream media, it quickly found its way into the cultural conversation. William Saletan of Slate.com, who remains one of today’s most relevant writers working on the issues of bioethics and human nature, jumped on the story with a very interesting essay that openly asked the question many others were more quietly asking: “If homosexuality is OK, why is incest wrong?”

After reviewing the various legal arguments used to justify criminalizing incest, Saletan comes to the conclusion that genetics cannot be the fundamental basis, since incestuous sex could be non-reproductive. Similarly, the basic issue cannot be consent, since no one is arguing in this case that the sex was non-consensual.

He gets the liberal response just about right: “At this point, liberals tend to throw up their hands. If both parties are consenting adults and the genetic rationale is bogus, why should the law get involved? Incest may seem icky, but that’s what people said about homosexuality, too. It’s all private conduct.”

Saletan comes to the conclusion that the basic reason for the wrongfulness of incest is damage to the family unit. As an Ohio court ruled, “A sexual relationship between a parent and child or a stepparent and stepchild is especially destructive to the family unit.”

Now, remember that Saletan raised the issue of the morality of incest as related to the question of homosexuality. He argues that the family-damage argument against incest does not apply to homosexuality. In his words: “When a young man falls in love with another man, no family is destroyed.”

Saletan’s argument is easy to follow, and if you accept his fundamental premise, it can even make sense. But his fundamental premise assumes that there is no damage to a particular family unit if a homosexual relationship exists. That argument can be made only by ignoring the impact upon a family of origin. Beyond this, it limits the family-damage argument to an individual family, when the argument must be more broadly applied to the family as an institution.

This article is a very interesting window into the sexual confusions that lie at the heart of our age. To his credit, Saletan gets the conservative argument basically right:

The conservative view is that all sexual deviance—homosexuality, polyamory, adultery, bestiality, incest—violates the natural order. Families depend on moral structure: Mom, Dad, kids. When you confound that structure—when Dad sleeps with a man, Dad sleeps with another woman, or Mom sleeps with Grandpa—the family falls apart. Kids need clear roles and relationships. Without this, they get disoriented. Mess with the family, and you mess up the kids.

That’s a pretty fair summary. Of course, the Christian argument goes much deeper than the merely conservative argument, affirming the fact that, with exacting precision, God has spoken to the sinfulness of such behaviors — specifically condemning both homosexuality and incest. In other words, Christians move the question from mere wrongfulness to sinfulness and place all issues of sin within the biblical account of sin and redemption.

It is extremely revealing that, for many of our fellow citizens, incest may merely “seem icky.” And yet, all around us are folks who, with a straight face, deny the inevitability of this slippery slope.