I don't think its right to judge the rationality of decisions based on their outcome. The question is whether war was a rational decision at the time. From a realist perspective anything decision is rational if it can lead to an improvement in the chances for survival. If war leads to a relative increase in my power even if I may lose soldiers and resources, then its worth it.
If country A has 100 soldiers while country B has 20 soldiers, even if the cost of war is a 2 to 1 loss in soldiers, war would result in the absolute power of country A.
In a conflict between two countries with nuclear weaponry, the core logic is the same, but the paradigm is different. Nuclear warfare can erase both countries off the face of the earth. This follows from the fact that to combat nuclear attacks, countries started adopting hair-string triggers to destroy the adversary before they can send more warheads their way... except now every country is doing the same thing. In this case, forget the relative nonsense, anyway you cut it, nuclear warfare is not rational for countries because it will end their survival.
My belief is that MAD is sound. And my underlying assumption is that countries tend to think rationally when dealing with international relations. Regardless of leadership, countries do whats best for them an overwhelming majority of the time. Case in point, how often has the U.S. (the bastion of freedom) voluntarily helped countries/people when the U.S.' interests were not directly involved? Also, observe how a seemingly crazy country like North Korea plays the game shrewdly by varying is strategy depending on its adversary.
I agree that there is a threat that nuclear weapons will get in the wrong hands and, in that case, I think its more than probable that disaster would ensue. But the safety and standards for handling infrastructure degradation has improved significantly since the early days of nuclear weapons (when many were lost to the ocean and never recovered) . As for Putin's threats, its nothing a good back and forth of denouncing and condemning can't fix.
But the distinction is that its wasn't the potential of losing Paris and Parisians that forced France to surrender. The French government judged that they had more to lose than gain from continuing to fight.
Maybe Hasegawa's interpretation has new implications regarding nuclear deterrence theory, but not how the author suggests. The idea that the nuclear bombings were not decisive factors in Japan's surrender does not mean that nuclear weapons do not serve as a deterrence. Nuclear weaponry advanced so much in the aftermath of WW2 that now nuclear countries can literally reduce entire nations to pixie dust. And the potential of MAD (Mutually Assured Destruction) all but guarantees that nuclear countries will never attack each other for fear of nuclear escalation.