No, the Nazis (even Adolf Hitler) were not monsters (evil or otherwise). They were human beings. Homo Sapiens. However, they were quite specific human beings.
They were national-sociopaths. And thus were driven by two very different kinds of emotions – genuine patriotic love for Germany and German people and by virulent fear of, and hatred for some other nations (first and foremost, the Jews). And for their political opponents in Germany as well.
A classic sociopath (by definition) is an individual who loves only himself (or herself for that matter) and cares only about himself/herself. He/she considers all other individuals as tools that he/she uses to satisfy one’s needs, wants and desires. Often with devastating consequences for the tool in question.
The ‘morals’ and ‘ethics’ of a sociopath are short and simple: What is good for me is good; what is not good for me is bad. What is good for me is Good; what is not good for me is Evil. Thus, a sociopath does not give a rat’s ass about needs, wants, desires, well-being and happiness of other individuals.
A national-sociopath, again by definition, is the one who is a genuine patriot of his/her nation, loves it dearly, has an irresistible desire to serve it to make his nation happy – and even is consent to die for his/her Fatherland, if necessary. But he or she sees all other nations only as tools (servants or even slaves) that he/she uses to satisfy needs, wants and desires of his/her nation.
Thus, a national-sociopath does not give a rat’s ass about needs, wants, desires, well-being and happiness of other nations. He/she views some nations as partners (to be used and exploited nevertheless), others as servants or even slaves (ditto) and some others as mortal enemies (to be ruthlessly exterminated).
And that’s exactly who the Nazis really were and that’s exactly why they did what they did.