Well, I do understand that the scientists who who were tasked with ensuring M.A.D. really was M.A.D. had to perform these tests out of more than mere curiosity, but like you point out, bigger and bigger bombs are only useful to a certain point, there are many more considerations beyond just yield. More generally, I've always been somewhat skeptical that M.A.D. makes us safer; I suppose one could say it prevented the cold war from becoming a hot war, but it certainly has done little to prevent conventional wars in general, and even if it might make angry despots or revenge-minded psychopathic leaders second-guess aggressive actions, it does so by risking the lives of thousand or millions of innocent civilians. I haven't seriously investigated what full-scale nuclear war would be expected to look like between Russia and the US, or India and Pakistan, or (theoretically) Israel, Saudi Arabia and Iran, so perhaps most of my conception is based on antiquated mass-media fear mongering. I suppose it's a little like gun control. Does everyone owning and carrying a gun make us all safer on a personal level, any more than every sovereign nation having a nuclear arsenal make global politics safer?