Rainsford was pushed through a very traumatic experience where he faced death at the hands of a fellow hunter in Connell's "The Most Dangerous Game." It is because of this traumatic view of being one of the hunted that Rainsford made one exception to his rule about not killing humans and that was to kill the one who hunted him. I would hope that Rainsford wouldn't take up hunting humans after he killed Zaroff; I think he made an exception for the deranged man who sought to kill other humans. Zaroff said at one point that Rainsford was "a righteous young man," thereby showing that Rainsford was not of Zaroff's same thinking. Of course, the author doesn't go into any detail after Rainsford takes over Zaroff's bed, so we cannot know for sure if Rainsford turns to hunting other men or not--hopefully not.