What if use of nuclear weapons really was, literally and actually, "unthinkable"?

What I mean here is a bit different from the Cold War scenario, in which Russia and the U.S. were extremely reluctant to use nuclear weapons because of the threat of mutually assured destruction. What I mean is a bit more like an instinctive inability to use nuclear weapons, regardless of immediate consequences. Because of some perception of the likely long term consequences -- annihilation of the human species. So, whether or not we feared immediate annihilation, we would fear long term consequences of a similar type, making it psychologically impossible to use nuclear weapons. Now, we can know what's going on in our own minds. But, not other people's. So, although we might know that we would never use nuclear weapons, we could never know with certainty that other people would not. So, even if no one could possibly use nuclear weapons, they probably would still be built, to use mutually assured destruction to be doubly sure. So, suppose that following the atomic bombings in Japan in 1945, everyone on the planet conceives, quite suddenly, that these weapons must never be used again. I think they still would be built. And, I think the H-bomb would still have been developed. However, the instinctive certainty that they could never be used again, would have changed things. The U.S. would be aware that its monopoly of the A-bomb gave it no real security. Hence, there would be less of an American demobilization after 1945 in Europe. The U.S. would feel the need for substantial military forces to balance off the Soviets. In China, the U.S. forces would become directly involved in the fight against Mao Zedong and the Communists. With no real nuclear deterrent, the U.S. cannot accept a communist China. The U.S. would be defeated, eventually, with massive losses in China, leading to an early decline in U.S. power in the world. Russian and Chinese communists would become dominant in the world by the mid 1950's. All of Indochina goes communist by 1955. A buildup of Western European military forces maintains an uneasy balance against the Soviet forces in Eastern Europe. In most ways the world's development parallels OTL, but, with less U.S. power, and more Communist Russian and Chinese power.