Because, a Slate columnist points out, “marriage is plastic”:
Just like heterosexual marriage is no better or worse than homosexual marriage, marriage between two consenting adults is not inherently more or less “correct” than marriage among three (or four, or six) consenting adults. Though polygamists are a minority—a tiny minority, in fact—freedom has no value unless it extends to even the smallest and most marginalized groups among us. So let’s fight for marriage equality until it extends to every same-sex couple in the United States—and then let’s keep fighting. We’re not done yet.
Stanley Kurtz call your office.