I agree with you, however, that he is generally portrayed that way. People seem to accept the good intentions of Stalinists, Maoists, but they certainly don't accept that Hitler meant to do anything of any value at all.
It may be because fascists rejected the principle of human equality completely.
That is a question that I have wrestled with for ages, and there is no easy answer to it.
I think that part of the answer may be understood, if we can understand why fascism is always presented as a "right-wing" ideology, when it is, in fact, just another variant of socialism.
In terms of being an absolute cause of human misery, Hitler was pretty small-time when compared to either Stalin or Mao. Yet he has the worse reputation. Was it because half of Hitler's victims were Jews, and much of the intellectual elite in this country is Jewish?
One aspect of the Hitler question that I find disturbing is that while Hitler, the man, has been rejected, the modern left still enthusiastically supports many of his ideas, e.g., his support for animal-rights and vegetarianism, or eugenics.