New York Times columnist Ross Douthat tries to explain his opposition to the legal marriage of two loving adults:

If this newer order completely vanquishes the older marital ideal, then gay marriage will become not only acceptable but morally necessary. The lifelong commitment of a gay couple is more impressive than the serial monogamy of straights. And a culture in which weddings are optional celebrations of romantic love, only tangentially connected to procreation, has no business discriminating against the love of homosexuals.

But if we just accept this shift, we're giving up on one of the great ideas of Western civilization: the celebration of lifelong heterosexual monogamy as a unique and indispensable estate. That ideal is still worth honoring, and still worth striving to preserve. And preserving it ultimately requires some public acknowledgment that heterosexual unions and gay relationships are different: similar in emotional commitment, but distinct both in their challenges and their potential fruit.

Let's say you think, as I suspect Ross Douthat might, that Christianity is “one of the great ideas of Western civilization.” Are we “giving up on” Christianity by allowing people to practice Judaism and Hinduism and Buddhism and Islam and Atheism? Repeal the First Amendment! Or let's say that you think democratic elections are “one of the great ideas of Western civilization.” Does it follow that it should be illegal to decide not to vote? Teachers are pretty important to Western civilization, too -- so perhaps we should make it illegal to be a police officer, bank teller, florist or ditch-digger?

Douthat is essentially arguing that if X is important, Y should not be allowed. For some values of X and Y (say, “Life” and “Murder”) that makes sense. For others (“Teachers” and “Firefighters”; “Christianity” and “Judaism”) it does not. Douthat makes no effort to explain why the marriage of two gay people belongs in the former category rather than the latter. And it seems not to have occurred to Douthat that his effort to preserve the “sexual ideal” of “lifelong fidelity and support by two sexually different human beings” actually demeans that which he seeks to protect, by suggesting that heterosexual marriage is so tenuous a concept that it cannot survive the extension of marriage rights to gay couples.

The American Prospect's Adam Serwer writes: “Ross Douthat's column this morning reads like a column from someone whose religious and cultural views lead them to oppose marriage equality but can't think of a very good reason for the state to prevent recognition of same-sex marriages.” That sounds just about right.