From the start of the debate on same-sex marriage and right up to last week’s Supreme Court ruling that legalized it nationwide, one of the most common arguments from the opposition has been the “slippery slope” to polygamy: If marriage can be redefined from a male/female union to a union of any two consenting adults, why stop at two?

Supporters of same-sex marriage have generally dismissed such arguments or mocked them as scaremongering. But there has also been a steady trickle of articles from the left asking what’s so wrong with legalized multi-partner marriages. Some even argue, as writer and academic Fredrik deBoer does in a recent Politico essay, that polygamy should be the “next horizon” of social liberalism.

Both the alarmists and the cheerleaders have a point when they say that the high court’s majority opinion in Obergefell v. Hodges, which emphasizes the freedom to marry, could be cited as precedent for recognizing polygamous marriages. But there are also solid arguments against such an interpretation. And there are many good reasons, practical and moral, that multi-partner marriage should not become a liberal cause.