In some respects, a reader responds to a book with his own intellectual, emotional and ideological makeup; liking, disliking, enjoying, approving is a function of the person that reader is. But there is another side of the coin: the reader also abandons in part his "practical self" (as aesthetically-minded used to call it sixty years ago) and tries instead a virtual self which is in part proposed by the work, as part of the experience it provides, and is also in part an unpredictable mixture of this guided experience, of personal tendencies and sympathies, and of unconscious, repressed or unacknowledged drives usually kept under leash in more "practical" activities. The virtuality of fiction allows us to experience virtual selves which roam free (in a sense) not just over time and space, following the guidance of the plot, but also over a moral landscape of good and evil intermixed and problematized. This unruly virtual self is to a good extent under the vigilance of the critical, moral, official self of the reader during the reading process, and the latter takes over by and large at the end of the work, but the emotional and ethical gymnastics of virtual experience (I include here both fiction and narrative at large) have done their job, and some cathartic effects have taken place. Or maybe some seeds of evil have been sown, it's a risky carnivalesque space where reality and the moral order are problematized, and that's why professional moralists have often distrusted fiction or warned against it. The fictionist or narrator is an experimental moralist, and there's no telling what may result form such experiments in morals. Some shaking and discombobulation, one would not be surprised.
(A comment to a post by Norman Holland, "How Novels Make Me a Murderer")