The talk of gay marriage brings up two points of grave political magnitude.
The first is that gay marriage evangelists are ready to take advantage of that clause in the Constitution (the "full faith and credit" clause) that requires individual states to respect legislation and judicial findings of other states in respect of citizens of those states. A couple who are married in the state of Virginia must be treated, when traveling in Wisconsin, as married. The Constitution (Article IV) does say that "Congress may by general laws prescribe the manner in which such acts, records and proceedings shall be proved, and the effect thereof."
That authority of Congress here is presumably evidentiary, not substantive. Certainly that position will be taken by those who will be citing Article IV as requiring every state to acknowledge as a marriage anything so deemed by the judiciary of the state of Vermont. One might rest easy at the prospect of Vermonters proceeding with their own tribal laws, but of course it would not be so. The Reno, Nev., formula would surely happen again. In the '30s, people who wanted to be divorced, even though the laws in the state where they lived wouldn't grant a divorce, traveled to Reno and came back with their full-faith-and-credit divorces.
These stratagems for avoiding the law in the state in which you live are challenged as never before by that juggernaut determined to go all the way with the license given by the Supreme Court's Lawrence decision, illegitimizing de jure anti-gay legislation. The idiomatic compression of the legal argument would read: Since they can have sex, why can't they marry?
We have then the full-faith-and-credit clause of the Constitution prospectively sanctioning a dramatic alteration in the basic social arrangements of the United States. Those who don't want such a change coming in from judicial syllogisms have now only the defense of a constitutional amendment.
Conservatives correctly tend to back off from such amendments. It is correct that amendments have frequently been proposed in the past to advance tactical objectives, among them the protection of the flag against desecration. But the test now should be framed differently. It is: How does a self-governing republic proceed with a judiciary that has taken to writing basic laws?