Deterrence is an abstract concept. Like the Holy Trinity, it must be believed; it cannot be proved. The trillion dollar nuclear spending program is based completely on belief, not evidence, because there is none. The fact that we haven't had a nuclear war does not prove that we won't have one some day. When it comes, it will not comfort anyone that we didn't have one for 60, 70 or 100 years.
If you lay out all the factors at play, there are enough unknowns to totally undermine confidence in deterrence. In any event, the thousands of nuclear weapons in the American arsenal are more than sufficient to "deter" if deterrence there can be.
In the 16th Century, many people bought "indulgences" in the belief that their time in Purgatory would thereby be reduced. Very smart and educated people believed this. They don't anymore. Nor will people believe in nuclear deterrence some day; either because we will wake up from this nightmare or because there will not be any "we" to notice!
Governor of California