"there really is no legitimate reason for building such a system"

False- ANY lives saved would be worth it.

beardedbruce, you have said that if any babies are killed by a nuclear weapon, the US will be obliged to destroy the entire world. So if even one nuclear armed missile gets through, NO lives will have been saved by this system.

On the other hand, if we do what is needed to make the world a less violent place, it simply won't be an issue.