BMD is a sham, period. It is based on the premise, never show to be held by an adversary, that limited nuclear war is possible. The is no possible capacity, driven by technology or the ability to finance it, that 100% of incoming warheads will be destroyed before detonation. Given the number of warheads expected to launch, either in an all-out attack of any form of "limited" engagement, one must expect at least 1% to 10% to hit their targets, and that may well be at the low end of estimates. Millions will die on either side, radioactive poisons will be spewed globally, and all societies disrupted. 
Nuclear war must never occur and it is the job of all politicians and diplomats to see that is the case. All other paths lead to ultimate disaster. 
Read Gwynn Dyer's  book "War" for an excellent history and analysis of BMD.