TODAY IS FLAG DAY, and this is an election year. It is no coincidence that the Senate Judiciary Committee plans this week to report out a constitutional amendment giving Congress the power to prohibit the "physical desecration" of the American flag. The flag-burning amendment is one of those regular rituals of legislative troublemaking that would be beneath comment save for the chance that it might actually muster the votes necessary to get sent to the states for ratification. The House of Representatives approved the amendment last year, as it always does, and supporters in the Senate fell only a few votes shy. Foes should have the votes to kill it again this year, but one never knows. In the long run, the threat that it will become a real blight on America's founding charter -- rather than merely on the honor of its legislators -- is a real one.

The problem the amendment purports to address doesn't exist: Flag burning is rare. The surest consequence of passing the amendment, in fact, would be to make it more common. Flag burning could become a particularly exciting form of protest were it an affront not merely to social norms and decency but to the constitutional order itself. But even if flag burning were rampant already, writing censorship of expression into the Constitution would still be offensive.

Burning flags is a particularly unpleasant form of expression. But the First Amendment protects many disgusting symbols: swastikas, cone-shaped white hoods, and hammers and sickles, to name a few. Creating an exception to the First Amendment for flag burners would probably not change the broad swath of its protection. But it would sap considerable vitality from the principle that lies at its core: that government doesn't get to decide which ideas -- and which modes of expressing them -- are beyond the pale.

Justice Antonin Scalia, who voted to strike down the statutory ban on flag burning some years ago, has described in speeches how doing so irritated him. He would have loved to put the defendant -- a "bearded, scruffy, sandal-wearing guy burning the American flag" -- in jail, he said. It made him "furious" not to be able to. But "I was handcuffed -- I couldn't help it, that's my understanding of the First Amendment. I can't do the nasty things I'd like to do." Other democracies still proscribe the expression of certain unpopular ideas, from race hatred to Holocaust denial to offensive speech about monarchs. The American concept of freedom, as Justice Scalia well expresses, responds to disfavored, even vile, expression with moral opprobrium alone, not the force of law. Those handcuffs must remain in place.