In their minds, the Aryan race, as the "master race", was to serve as the head of the body of humanity, directing, judging and engaging in intellectual activity. The inferior races were to serve as the hands, arms, torso, legs and feet of the body, toiling away to provide sustenance to the Aryan head, which required the heaviest resource load, just as the brain requires by far the highest density of bodily nourishment. Jews, dissenters, homosexuals, and other classes of people were seen as cancerous parasites that needed to be removed to make the body of humanity healthy once again.
It does act "to the betterment of humanity". It just doesn't care one bit about humans as individuals.