FDR had no illusions about what immense and unnecessary suffering Stalin’s domestic policies produced, but this wasn’t FDR’s business. US national security was.
Without the immense sacrifices by the USSR, Hitler would almost certainly have won WWII and Americans be living under Nazi rule, but the owner of the ‘investments’-firm airbrushes Russia totally out of the Allies’ victory.
The problem isn’t that Truman often misunderstood, but that he surrounded himself with people that his Party’s top donors liked. Truman wanted to be a progressive but ended up being only a liberal.
Americans must strive for complete and honest analysis of the past (and present) conflicts. And if she is to remain true to her own ideals, America must strive for more noble and moral ends—in all conflicts, domestic and foreign—guided by our most cherished first principles, such as the Golden Rule.