The best that can plausibly be claimed for the national missile defense scheme currently proposed by the United States is it would provide unreliable protection against an improbable form of threat. However well the proposed system might perform in controlled tests, it always would have to be assumed a strategic opponent capable of developing a long range ballistic missile would also be able to equip it with penetration devices likely to be effective under operational conditions. Of course, a "state of concern" (the new name given to states formerly known as "rogue") would presumably bypass the envisaged system with more readily concealed means of attack. The entire project promises to stimulate threats it cannot handle.
Therein lies the reason it is considered to be so provocative. No one is prepared to believe the United States or more precisely, its decision makers is now or would forever remain that stupid. Potential strategic opponents are compelled to assume the nonsensically limited system is but a stalking horse for a more serious effort, and the principal U.S. advocates of ballistic missile defense loudly encourage that assumption. The initiative is interpreted, moreover, in the context of very assertive plans for further elaboration of the already imposing offensive capabilities of U.S. forces. Against an initiating opponent who can choose the timing and operational details of an attack, the proposed U.S. system is basically worthless. Against an opponent who had first been subjected to a U.S. attack, an expanded version of the proposed system could be a very serious matter indeed the final element needed to establish decisive, intimidating superiority. The real issue in question is the balance of offensive capability and more generally the fundamental terms of international security.
John Steinbruner is the Director of the Center for International Security Studies at Maryland.