Nonetheless, many supporters of the same-sex marriage decision reject the possibility of plural marriage with surprising confidence. Writing in Slate after the decision in Obergefell, Judge Richard A. Posner of the United States Court of Appeals for the Seventh Circuit rejected a right to plural marriage because it would lead to gender imbalances if “the five wealthiest men have a total of 50 wives.” Similarly, the same-sex marriage advocate Jonathan Rauch has argued that polygamy allows “high-status men to hoard wives” and destabilizes society.

Gender equality is of course a serious concern. But the arguments above rest on the assumption that plural marriage will involve only one man and multiple women. That assumption is weak. Plural relationships could well be (and in some circles today are) between multiple people of both sexes, not all of whom are strictly heterosexual.

True, most past episodes of plural marriage have been patriarchal. But the lesson of the same-sex marriage case is that we should not be too wedded to historical assumptions. It was not that long ago that many people held vicious stereotypes about same-sex relationships that led them to wrongly assume that gay people were unfit for marriage. We should not make the same mistake in assuming we know what plural marriages in the future would be like.