You offer the pair of Hitler/Mussolini vs. Stalin/Chiang Kai-Shek, and you suggest their evils are comparable. Maybe. But in each pair, there's a clear stand-out (Hitler killed a lot more than Mussolini and Stalin a lot more than Chiang.) And there were clear reasons for preferring each leader over the alternatives. Stalin killed a lot, yes, but he killed mostly his own at a time when leaders like Hitler and Mussolini were meddling in Europe and Africa, threatening Western countries' interests. The Soviets never proved a threat to the West until after they got the bomb. Even Mussolini, who was a brutal and merciless politician, actually presided over a country with remarkably few executions - his brutality within his own country was not the reason for the Allies' enmity with him. It was his attempts to craft a new Italian empire, which inevitably came into conflict with Allied powers' interests, and his alliance with the demonic Hitler, that got Mussolini his reputation for evil. And take Chiang Kai-Shek. Though it's true he ended up being a repressive dictator in Taiwan, and during his time in the mainland he squandered plenty of resources fighting the Communists as opposed to the Japanese, we never actually minded that. Chiang Kai-Shek, after all, ended up killing a HELL of a lot fewer people than Mao. Mao rarely even actually meant to kill as many as he did, but it was the nature of his ideology that when he messed up his communalization efforts, millions of his own people starved to death.
Turkish warplanes attack PKK targets after soldier killed in attack (Reuters)