In a New York Times “Room for Debate” discussion on plural marriage, John rebuts the slippery slope:
Polygamy raises a number of public-policy concerns that same-sex marriage does not. That said, the gay-rights movement has bolstered the polygamist-rights movement in one key way: by insisting that finding a practice weird or icky or religiously anathema is not sufficient reason to make it illegal.
Read his full post, and watch the accompanying video, here.