Carson Hallowoy argues in The Public Discourse that "The oral arguments on Proposition 8 at the Supreme Court suggest that there is very good reason to believe that the declaration of a “right” to same-sex marriage will set us on the path to polygamy":

Opponents of same-sex marriage resist it because it amounts to redefining marriage, but also because it will invite future redefinitions. If we embrace same-sex marriage, they argue, society will have surrendered any reasonable grounds on which to continue forbidding polygamy, for example.

In truth, proponents of same-sex marriage have never offered a very good response to this concern. This problem was highlighted at the Supreme Court last week in oral argument over California’s Proposition 8, the state constitutional amendment that defines marriage as a union of a man and a woman.

Surprisingly, the polygamy problem that same-sex marriage presents was raised by an Obama appointee, the liberal Justice Sonia Sotomayor. Sotomayor interrupted the presentation of anti-Prop 8 litigator Theodore Olson to pose the following question: If marriage is a fundamental right in the way proponents of same-sex marriage contend, “what state restrictions could ever exist,” for example, “with respect to the number of people . . . that could get married?”