Some states, for instance, allow marriages between first cousins; others forbid it. Some states allow 15-year-olds to marry with parental consent, while most set the minimum age higher.

And the feds? They have consistently observed a policy of staying the hell out. Washington doesn't tell Colorado and New York which marriages it will acknowledge. Colorado and New York tell it.

Not so with same-sex unions. Under DOMA, the federal government insists that some marriages are not marriages.

That's particularly hard to justify because the other major provision of the law bends over backward to protect state authority over matters marital. It says no state is obligated to recognize a same-sex marriage that took place somewhere else. Gays married in Vermont magically become single when they venture into New Hampshire.

This part of the law goes beyond the norm to accommodate different preferences. Usually, states are obligated to enforce contracts made in other states. Back in the segregationist years, Southern states often honored interracial marriages transacted beyond their borders even though they regarded them as "so unnatural that God and nature seem to forbid them."

Given the strong feelings about gay marriage, the local option is the best option. States that abhor the idea should be free to implement policies reflecting that sentiment. But the other side should have exactly the same prerogative: giving both heterosexual and homosexual couples access to marriage in full.

Our system, unlike Mao's China, is supposed to let a hundred flowers bloom. But for the best growth, the federal sun has to shine on all of them.