How could FDR and Truman fail to recognize the abhorrent and murderous nature of Stalin? How did they fail to see the millions murdered and enslaved in the USSR? How did they manage to ignore the fact that Stalin aligned with Hitler in '39 and then conquered half of Poland, the Baltic States, and invaded Finland all before we entered the war? FDR even buried intel reports regarding the Soviets assassination of the Polish officers at Katyn because he did not want to offend Uncle Joe. We must realize that FDR was a radical leftist who liked Stalin, but hated Hitler. The hypocrisy of his beliefs are amazing, but typical of leftists then and today.
Again, we should not have aligned with the Brits and the Soviets. We should have stayed neutral. The result of our neutrality could have resulted in a stalemate in the east and ultimately an end to the war. Thus leaving Stalin and Hitler contained. And lots of 18 year old American boys alive.
I think its a speculative claim that our nuetrality would have resulted in a stalemate in the East. I think there would be plenty of arguments to be made that it would have resulted in the entire European continent being dominated by the Soviet Union.