It might be argued that communism was as bad as nazism as a treat to mankind. In you forget the german naturalist ideology, they both proceeds the same : makes advantages of an economic crisis to give birth to a will of change in the lower classes, reject all the fault to the act of a group of people, so you are enforcing your followers, then when elected, take over the medias and makes subtile changes to the democracy in order to be sure to lead to a dictatorship while being advertized as someone making deep changes to lead to a better society. While this first step is done, enforces your domination, by not only controlling medias, but also starting propaganda and stuff like this... On the other hand, ensures you have gathered all powers. And voila, Hitler and Staline being boths dicators in no time.