Traditionally, strategic offensive arms control and ballistic missile defense have been viewed as mutually exclusive. During the Cold War, the general belief was that anti-ballistic missile (ABM) systems would call into question the ability of the superpowers to successfully survive a first nuclear strike and inflict sufficient damage with a second strike. That is, missile defense could allow one superpower to launch a first strike and then use its defenses to intercept a second strike with the other superpower's surviving warheads--thereby undermining deterrence and stability. Furthermore, the thinking was that this situation would result in a dangerous offensive arms race as each side sought to counter the effects of the other's defenses.
That logic had some merit during the Cold War. However, opponents of national missile defense (NMD) continue to cling to the outdated Cold War rationale and ignore or disregard the emerging ballistic missile programs in rogue states as a real threat to U.S. national security. Ardent supporters of missile defense argue that we should abandon the ABM Treaty to deploy missile defense--largely because they want to deploy a global rather than a national missile defense. Neither is correct.
The most prudent path is to pursue development of a limited NMD system to defend against rogue state threats, simultaneously renegotiate the ABM Treaty with the Russians, and continue further strategic arms control negotiations under the Strategic Arms Reduction Treaty (START) process. In fact, the Russians have intimated that they might be willing to accept changes to the ABM Treaty to allow for a limited NMD in exchange for even deeper cuts in strategic offensive forces.
The NMD system that makes the most sense for countering threats from rogue states is a limited ground-based system. Such a system should provide sufficient defensive capability against threats from rogue states but not pose a serious threat to Russian retaliatory capability. If the United States changed its nuclear doctrine from war fighting to deterrence, deep mutual reductions in offensive forces to levels below the START III framework agreement (perhaps as few as 1,500 warheads) would still allow the United States to deter Russia and smaller or emerging nuclear powers. Such a reduction combined with a limited land-based NMD would greatly enhance U.S. security.