As I’ve outlined, I think that the claim that state laws that define marriage as the union of a man and a woman are unconstitutional is preposterous. Not that I expect such a consideration to deter five willful “living constitutionalists” from embracing a position that even the most left-wing of the Warren Court justices regarded as frivolous.

In “Memo to Supreme Court: State Marriage Laws Are Constitutional,” Gene Schaerr and Ryan Anderson spell out why, under the constitutional design of federalism, the Court ought to recognize that states have authority to retain the man-woman definition of marriage (just as they have authority to abandon it). An excerpt from their conclusion:

The only way one can establish the unconstitutionality of man–woman marriage laws is to adopt a view of marriage that sees it as an essentially genderless, adult-centric institution and then declare that the Constitution requires that the states (re)define marriage in that way. In other words, one needs to establish that the vision of marriage our law has long applied is just wrong and that the Constitution requires a different vision entirely.
There is, however, no basis in the Constitution for reaching that conclusion….