Is polygamy the next step in the redefinition of marriage? Jillian Keenan writes in Slate that we should legalize polygamy, and adds that “No, I am not kidding.” Frederik Deboer, writes in Politico that: “it’s time to legalize polygamy.” And he adds, “group marriage is the next horizon of social liberalism.” They remind us that many people (from Rick Santorum to Bill O’Reilly to Tony Perkins) have been warning that legalizing same-sex marriage will lead to polygamy and polyamory.

The moral and legal argument for polygamy is now very simple. First, acknowledge that a redefinition of marriage does not have to stop at two. Chief Justice John Roberts in the recent same-sex marriage decision pointed out that even though the “majority randomly inserts the adjective ‘two” in various places, it offers no reason at all why the two-person element of the core definition of marriage may be preserved while the man-woman element may not.”

Second, the same-sex marriage decision was based in part on the belief that society has shifted in its opinion about marriage and the same could be true about shifting opinions about plural marriage. After all, why should the sexual revolution stop at same-sex marriage? For that matter, why should it even stop at polygamous marriage?

Third, the law should not discriminate against minorities. Already thousands of Muslims in America live in polygamous families. The man marries one woman in a legal ceremony and other women in a religious ceremony. The case could easily be made that the other women deserve legal protection as well.

The current debate about polygamy demonstrates that those who predicted that same-sex marriage would lead to polygamous marriage were right. This is what happens when you redefine marriage.