Andrew Sullivan writes on Canada legalizing gay marriage: "Opponents will have to base their arguments in future on actually tearing existing marriages apart. What a conservative idea!"
That's some new ground in circular reasoning there. If something you oppose comes to pass, then your continued opposition to it will violate your stated principles. Doesn't seem like a winning argument to me.
That's sort of like saying that if restrictions to abortion are passed, than pro-choicers will have to base their arguments on saying that people alive should have been aborted. It may make me feel better, but it's not a convincing argument.