Because the sides (which, to be clear, were mostly USSR vs nazi germany) were clearly not equally "morally and ethically bankrupt"?
USSR, while very far away from perfect as I will be the first to admit, was a socialist nation struggling to build an equitable, just, and advanced society for all working people, first inside its borders then worldwide.
Germany was a bunch of rich capitalists pushing nazi propaganda on its population, aiming to turn the entire European continent into an ethostate, enslave all slavs and kill all jews, with reactionary&inhumane views about gender, sexuality, disability, and a thousand other topics.
If you think that those two sides are somehow "the same" and thus it's somehow OK if Germany won that war, why would USA vs Iran be different?