The Gentle People are ambiguous; they do frightening deeds and benevolent deeds, force those in their thrall to commit murder but also help out around the house. They represent a worldview that is violated in both good and bad directions, one with unexpected misery but also unexpected boons. A widespread subversion myth, however, suggests a worldview that is mostly violated by bad experiences. The motion from ambiguous, inscrutable mythic beings to purely evil mythic beings is notable. One possibility is that it accompanies a worldview that is much too nice and positive, and hence mostly needs gap filling when bad events occur. It may be a feature of the Experience Machine that it co-exists with. The more utopian the vision, the more purely evil the gap-filling creatures must be.
Another possibility is that it is a feature of the experiences that get through and affect people - a feature of the experienced world - rather than a feature of the theory. A theory will need more patches for bad information if the world gets a lot worse, even if the theory remains the same.