You do not see any difference between genocide and reacting to a belligerent power? If we had attacked germany and/or japan without provocation, your argument would be relevant. As Germany and Japan were actively trying to conquer all those around them, fighting back is self defense. The point of war of that sort is to degrade the enemies ability, through infrastructure, personnel, and moral, to perpetuate war.
Even at the time, the targeting of civilian targets was controversial, and there were many who were against it. There wa not a monolithic mortality of the west that said that killing civilians was okay morally, there were hard choices to be made in order to protect civilians in other countries from being killed by the belligerents.
No, it’s because the western powers had very little power over what happened to soviet soldiers. There were discussions of bringing up the atrocities committed by soviet troops, but in order to punish them, we’d have to go to war with the Soviet Union. The morality of the soviet union allowing their soldiers to go unpunished is certainly questionable, but that is also one of the many reasons that the west and the soviet union parted way after WWII, we didn’t like their morals.
This is true, and the question is is do we want to improve the social contract, or let it devolve. To believe that morality is entirely neutral, and that one can only be judged by the morals that one subscribes to is nihilism.
We can have an academic philosophical debate about the intersections of morality and nihilism, of authoritarianism vs anarchy, but that is a deliberate side track from the discussion that we are trying to have, “What morals should we be subscribing to, to increase the chances of living in a fair and peaceful society?”