FDR, Churchill, and Stalin
Sometimes, it becomes necessary to hold your nose and support someone as reprehensible as Stalin if that's what is necessary to defeat a Hitler. As the staunch anticommunist Churchill said following Hitler's 1941 invasion of the Soviet Union, "My dear boy," he said, "if Hitler were to invade Hell, I would at least make a favourable reference to the Devil in the House of Commons!"
Sometimes, grown ups have to make difficult decisions. Too bad you're incapable of seeing such things.