There is no way that this is a no-brainer. There have been plenty of people across history who have murdered people for being different based on race, religion or any number of factors really, and 6 million or however many that he killed is not the highest number of dead in a mass killing in history so there is no reason to assume he is the worst of all-time. He is probably just the one who came closest to realizing his vision.
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http://soundcloud.com/thundersheep/verr-ckt-nach-liebe
http://soundcloud.com/thundersheep/lunatic-asylum