The Nazis were worse - as bad as the Soviets were - and they were evil - they did not make lamp shades out of people or develop methods to make soap out of human fat or felt fabric out of Jewish hair.
I am not a big defender of FDR, but I know of no better way to defeat Nazi Germany than to keep the Soviets in the game, just as keeping the Nationalist Chinese fighting was important to the defeat of Japan.
Of the Mass Murderers of all time:
1. Stalin: 50 million
2. Hitler: 30 million
3. Mao tse-Tung: 20 Million
4. Chang kai-Chek: 15 Million
Poor China, having 2 of the top 4.
The 50 million to be killed by Stalin would be sooo relieved to know that their dead bodies would not be turned into lamp shades and -- soap.