Nietzche broke from the metaphysical basis of prior Philosophy and adopted a empiricist perspective on human interactions. Nature possesses no moral imperatives, but delineates animals on a spectrum of increasing complexity, between predator and prey. His concept of the Superman represented, in his mind, the more 'evolved' (amoral/ambitious/unsympathetic) Man, while the Untermensch represented man's instinctive Will to Power as having been subverted by superstition, subservience, pity or general stupidity. But I think he failed to realize that empathy and pity were memes which arose from Natural Selection, in order for any herd (or society) to function as a whole ; that if everyone considered themselves to be the 'Superman', you end up with an Ayn-Randian Objectivist solipsism or Fascism, both of which are essentially collective sociopathy on a grand scale. Since Nietzsche associated strength with a lack of empathy, and weakness with the altruistic impulse, it would be fairly easy to see him as a sociopath (his hermetic lifestyle and encroaching insanity may have accelerated this). However, he was known to show kindness to members of his immediate family, had romantic infatuations and friendships, and (anecdotally) protected a horse from being beaten to death by wrapping his arms around it. He seems to have been a mass of contradictions, at any rate.