Add same-sex marriage as an issue that now divides the country both intensely and evenly—and is therefore an issue that ought not be resolved one way or the other until public preferences become more settled. This is a reason why the Defense of Marriage Act (1996) and the proposed Federal Marriage Amendment (2003-04) were unwise, for they sought, prematurely, to declare victory for supporters of traditional marriage before public opinion had settled firmly in their favor. It is also a reason why the Supreme Court ought not declare a national constitutional right supporting same-sex marriage, for that would, prematurely, declare victory for supporters of marriage equality before public opinion has settled in their favor.
…the legal case for such a constitutional right is an excellent one. But the legal case for a constitutional right for different-race couples to marry was an excellent one in the wake of Brown v. Board of Education (1954)—but it took the Supreme Court half a generation to recognize such a right, in Loving v. Virginia (1967). In 1954, three-fifths of the states barred such marriages; by 1967, only southern states did so. Only after the stakes were lowered was it politically prudent for the Court to announce a national resolution.
– Yale Law professor, William Eskridge, explaining why the Supreme Court should “tread lightly if it considers the merits of a constitutional right to same sex marriage.”