I have no particular interest in wading through Richard Posner’s critique of the Roberts and Alito dissents in the marriage cases. But now that I see that Jonathan Adler points out one error Posner made, I’ll highlight another that jumped out at me. Posner writes (underlining added):

John Stuart Mill in On Liberty drew an important distinction between what he called “self-regarding acts” and “other-regarding acts.” The former involves doing things to yourself that don’t harm other people, though they may be self-destructive. The latter involves doing things that do harm other people. He thought that government had no business with the former (and hence—his example—the English had no business concerning themselves with polygamy in Utah, though they hated it). Unless it can be shown that same-sex marriage harms people who are not gay (or who are gay but don’t want to marry), there is no compelling reason for state intervention, and specifically for banning same-sex marriage. The dissenters in Obergefell missed this rather obvious point.

Posner, alas, is displaying his characteristic sloppiness. The dissenters did not miss the point. They instead expressly disagreed with it. As the Chief Justice puts it (underlining added):

Then and now, this assertion of the “harm principle” sounds more in philosophy than law. The elevation of the fullest individual self-realization over the constraints that society has expressed in law may or may not be attractive moral philosophy. But a Justice’s commission does not confer any special moral, philosophical, or social insight sufficient to justify imposing those perceptions on fellow citizens under the pretense of “due process.” There is indeed a process due the people on issues of this sort—the democratic process. Respecting that understanding requires the Court to be guided by law, not any particular school of social thought. As Judge Henry Friendly once put it, echoing Justice Holmes’s dissent in Lochner, the Fourteenth Amendment does not enact John Stuart Mill’s On Liberty any more than it enacts Herbert Spencer’s Social Statics. See Randolph, Before Roe v. Wade: Judge Friendly’s Draft Abortion Opinion, 29 Harv. J. L. & Pub. Pol’y 1035, 1036–1037, 1058 (2006). And it certainly does not enact any one concept of marriage.