Important to clarify that he attacked The Soviet Union. That government and power structure was engaged in a major slaughter of traditional Russian culture; as such, Hitler may not have had as much trouble with "Russians" (though anti-Russian racism may have played a role as well), but more with a system that he perceived as antithetical to his more socially conservative vision of society.

From a strategic military standpoint, yeah, huge mistake. Funny how western Europeans can't seem to get out of their own way, instead underestimating the power of the Russian people again and again and again...