Maybe, Steely, but the Moscow system protected just a single city with, I believe, a terminal phase intercept. You'd need an uneconomical number of 10 kt devices to defend all of your important military and industrial sites, not to mention against counterforce attacks. Sure, you can reduce the number of interceptors by using a system with midcourse intercepts, but that runs into feasibility issues (as the GMD program indicates). I think it's much easier to defend against a counterforce strike by siting most of your nukes on subs or mobile launchers than making a pricey and largely ineffective system.

I don't disagree that missile defense does change the underlying strategic calculus. I just think it's not a very cost-effective way to do so.