Stating the argument simply, if someone wants to torch Old Glory, I say let him be an ungrateful, misguided fool. In America we allow people to be ungrateful, misguided fools.
But there are more sophisticated ways of getting to the same place. I'm just too tired to list them all right now. Fortunately, Mark Steyn makes the case superbly here. You are hereby urged to read the whole thing.
UPDATE: Thanks to Power Line, this story is lots of fun. It's about a flag-burning incident involving former Major League Baseball player Rick Monday back in 1976. Read it here. If you like baseball you'll enjoy the story no matter what you think of the politics involved.