The TREATY obligations are that if the US or any treaty signatory is attacked with WMD, the US will reply with WMD. If 1 missile is launched, we have a very high likelyhood of being able to intercept it. If 25 are launced, we have a good chance to eliminate 10 - 20 of them, reducing the loss of life ( in the US or our ally) by 40 - 80 %.

But you keep saying that if there is a nuclear attack, the whole world will be destroyed. Are you now saying that if a missile gets through our missile shield, and a city in one of the countries we have this treaty with is destroyed, it won't result in the destruction of the entire world?

Recall that a single missile from a Nuclear power ( China, Russia, etc) can have 8 - 12 MIRV warheads, probably on the order of 250Kt each. A missile from a terrorist group or rogue nation would probably have one warhead, in the 20 -50 KT range.

It seems likely that a rogue nation or terroruist group would have access to a limited number of systems, while the nations that you claim would be threatened because they would lose their deterrence would have the number to overwhelm the defensive system- Thus it DOES NOT destabilize the balance of power, just defend against rogue states and terrorist groups.

This is wild speculation on your part, beardedbruce. It is far more likely that if a 'terrorist group' wants to deliver a nuclear weapon, they won't try to use a missile to do it, and that if we had the kind of system you are advocating, that would guarantee that they would use a non-missile way to deliver a nuclear weapon. So if 'terrorists' are the ones we are concerned about, the only way to reduce the possibility of deaths due to nuclear attack from such groups is to work toward eliminating the injustices that result in the existence of terrorist groups in the first place.

The term "rogue state" is one that we use when we want an excuse to destroy a country and its sovereignty. We don't label countries "rogue states" because they pose a legitimate threat to us. In the case of Iran, for instance, if we had been concerned about a possible threat from them, we would have accepted their offer to negotiate. We are labeling Iran a "rogue state" because we need an excuse to attack them and destroy their country and their sovereignty. And this is why we want first strike capabilities against such countries. We want to be able to attack Iran without having to suffer any repercussions of a nuclear nature.