This week on Public Discourse, Justin Dyer explains the jurisprudential missteps that lead some to think traditional marriage is unconstitutional:

...The Ninth Circuit Court of Appeals recently held that California’s traditional definition of marriage, approved by a voter referendum in 2008, is unconstitutional under the Fourteenth Amendment’s Equal Protection and Due Process clauses, and some legal commentators expect that the Supreme Court will soon take the opportunity to overturn the traditional marriage laws remaining on the books in forty-three states. Such a prospect, as a matter of constitutional law, would have been unthinkable only a decade or two ago. What happened?

... The new conception of liberty underpinning Lawrence made biological sex irrelevant to coupling and dissociated sex from reproduction, child-rearing, and the like—leaving traditional proscriptions of non-marital sex standing on shaky constitutional ground. And so it would seem, as Antonin Scalia noted in dissent, that the Court’s opinion also dismantled “the structure of constitutional law that has permitted a distinction between heterosexual and homosexual unions, insofar as formal recognition in marriage is concerned.”

... Whether the Supreme Court or history will settle on same-sex marriage in this way remains to be seen, but there is one reason to suspect it will not: the rationale for same-sex marriage undercuts the very reasons why we have a public institution called “marriage” in the first place. The old definition of marriage supposed that men and women were complementary by nature and that the state, barring some case of neglect or abuse, had an interest in legally binding fathers and mothers to each other and to their children. On the old account, to say marriage was between a man and a woman simply followed from what marriage, according to its nature and public purpose, is.