For many years, we have relied implicitly or explicitly on nuclear deterrence to prevent those with competing interests from leveraging their own WMD against us. Indeed, this idea is so elastic that it was not necessary for us to know with certainty from whom or from where we were attacked in order to successfully deter the attack. Should NYC disappear in a mushroom cloud, our missiles would be launched against the Soviet Union – case closed.
The idea worked because directly or indirectly, the USSR would have been responsible for such an attack. Since this was so, we could be certain of the necessity and target of the response in the calculus of MAD should we forgo the option of complete and immediate capitulation. Otherwise, we were content to know that somewhere in the Australian outback, life could go on after a nuclear exchange.
Given these well-defined imperatives, we could respond rationally to variations of a theme. If the attack was accidental, the retaliation could be limited to perhaps a single enemy city. The rule being “You break it, you bought it”. This rule tended to enforce the necessary caution and discipline when handling the Bomb. WMD were not a right – they were an awesome responsibility. As we later learned from the Soviet invasion plans of Europe, this was so much so that there was no escape either for France. Logic would not permit a half-invasion.
Should the competing interests not be so great that one would want to sacrifice the homeland, a limited regional nuclear war was possible – this was the purpose of the Pershing missile and Soviet SS-20s. All contingencies were predicated on the fact that the consequence could be linked to the responsible party. Thus, deterrence was rational.
Proliferation changes the entire equation. We must roll back time, adapt, or go the way of the dinosaurs. There is no other alternative - just dumb luck