Nazi racial theory is probably one of the most ridiculous things every thought out, which actually gained acceptance by anybody apart from the lunatic fringe.
The reasons why this is ridiculous is firstly; humans genetically are much more similar than say our closest relatives chimps are. In fact all of humanity is descended from a few thousand people who lived 70,000 years ago. Secondly; the Indo-Iranian peoples to describe themselves invented the term ‘aryan’, it meant basically noble or civilized. Although this term could go back to the Proto-Indo Europeans who probably lived in the steppes north of the Black Sea in the Ukraine. That makes some sense, for example; the Slavic languages (which originated in Poland and Belarus) are quite conservative, nowhere as near as the Baltic languages are although.
Thirdly; The Germanic peoples never called themselves Aryans, also Proto-Germanic has a lot of influence (loan words and sound changes) from a non Indo-European language it replaced in what is now Northern Germany and Denmark. Fourthly, while Sweden has the largest proportion of the population who are Blonde in the world, places like Poland, The Belarus and The Baltic Countries, probably have the same proportion of the population who are Blonde haired. Even many Nazis noticed in occupied Poland that the Poles were more ‘Aryan’ than the Germans were.