Last week, President George W. Bush officially announced that the United States would withdraw from the Antiballistic Missile Treaty. The decision was long anticipated. Mr. Bush and others in his administration never concealed their disdain for the treaty. But the inevitability of the decision makes it no less regrettable. Missile defense's effectiveness is unknown at best; strategic instability is guaranteed, however. Worse, this withdrawal from an arms control treaty sets an ugly precedent.

For many in the U.S., the 1972 ABM Treaty is a Cold War relic that has outlived its usefulness. For some advocates, missile defense is an opportunity to end the reign of Mutually Assured Destruction, an amoral -- if not evil -- doctrine that placed strategic value in mutual suicide. For others, a missile shield is the fulfillment of the dream articulated in the 1980s by then-U.S. President Ronald Reagan. For yet others, missile defense minimizes the threat from "rogue states" that are said to be resistant to the logic of assured destruction that would follow any missile attack against the United States.

For critics, missile defense is a pipe dream. The technological requirements of "hitting a bullet with a bullet" are too demanding. Most tests to date have failed, while successes have come under circumstances so rigidly controlled as to be unrealistic. Countermeasures and alternative delivery systems can be used to beat the system. All it takes is one missile to sneak through to prove the defenses a failure.