I can't agree with you in some aspects, Dark. Stalin's trust was obviously wrong, but not absurd. He, as we all do up to a certain extent, judged others after his own character, and old Iosif was clever, patient and cold. He would never have attacked the Soviet Union before finishing Britain (a very logical idea) and he couldn't believe that Hitler was going to start of his own will a war in two fronts.
But Hitler can have been clever, but certainly he wasn't cold and he didn't have any patience whatsoever...
You could say that Hitler and Stalin did really personify their political systems and ideas. Marxism presented itself as a Science, appealed to reason, glorified logic and believed that given time its victory was unavoidable. Fascism/Nazism appealed to the emotions, glorified will above all things and believed that only fast, violent action could avoid defeat.