Polyamory harms marriage. Its mainstreaming by some would erode everyone else’s ability to understand and live out true marriage. As the late Oxford philosopher Joseph Raz, whose views on sex and marriage were much more liberal than ours, nevertheless conceded, “monogamy, assuming that it is the only valuable form of marriage, cannot be practiced by an individual. It requires a culture which recognizes it, and which supports it through the public’s attitude and through its formal institutions.”

A recent article in the New Yorker paints a rosy picture of the many ways that polyamory and non-monogamy are making inroads into American culture. Amid a great deal of wishful thinking, one claim stands out: that opening your marriage to additional sexual partners can make it stronger. The New Yorker article notes that non-monogamy “is increasingly being presented not as a threat to bourgeois marriage but, rather, as a way to save the institution and all that it affords.”

This claim would be laughable if it weren’t being taken so seriously. It’s a bit like the infamous (and apocryphal) claim from an American military officer in the Vietnam War that “we had to destroy the village in order to save it.” Marital infidelity strikes at the heart of marriage, at its total commitment, expressed in vows of permanence and exclusivity. Spouses who engage in sexual non-monogamy, even if they act with each other’s consent, undermine the basis of an authentic and honorable marriage. And when their actions are public, and especially where they are publicly affirmed and celebrated, they further wound the culture of marriage that everyone benefits from when it is secure and flourishing.

Consider, by analogy, friendship. An ordinary friendship has a certain structure and point. In a true friendship, each friend wills the good of the other for the sake of the other. Without this goodwill, there is no friendship. As it weakens, a friendship withers.

Now, imagine that one friend, upset at the other for some perceived wrong, speaks maliciously of his friend behind his back, impugning his character. We would all have to admit that this action was a betrayal of the friendship, defying the norm that each friend acts for the other’s good.

But now imagine that the slanderer’s goal was to blow off steam over the perceived wrong and then return to the friendship with less resentment. If he is successful in this goal, someone might say that “the slander saved the friendship,” but this would be a mistake. The friendship was not saved, because the unrepentant friend stopped willing the good of the other, the very thing that made them friends. The opposite impression depends on a mistake about what friendship is—the deeply mistaken (and harmful) assumption that it’s most fundamentally a matter of feelings, not wills.

Now compare this to marriage. Like friendship, marriage has a structure and point. This structure is not subject to endless revision and modification but is a function of basic aspects of human well-being and fulfillment. As Western law and culture historically recognized, marriage is a two-in-one-flesh (“conjugal”) union of husband and wife. As a distinctive human good, marriage is an all-encompassing union.

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