I think that we humans find it hard to conceive such humongous changes in the world around us. We're used to a certain background in our lives and under-estimate the likelihood of any scenario that changes that a lot. Evolutionarily this makes sense: if you always think that the things you've never seen changing will never change, you will be right almost all of the time (and I could just as well call you myopic for not believing _my_ scenario).
But at the same time if instead of going with your instinct of how likely it is that such an outrageous scenario would occur, you instead follow simple game theory, there is only a few ways out of this situation, at least that I can think of:
A) The USA says We acknowledge your concerns and and actually, we're not gonna build that shield after all (or some variation of this)
B) Russia says Actually, I'm just gonna lay down and be bullied into irrelevance
Do you see either of these happening? Things will have to get much worse before either of these happens. Do you see other alternatives?