Dr. M. Scott Peck (Road Less Traveled) wrote a book, People of the Lie: The Hope for Healing Human Evil, which declares that evil people truly exist. Kingdom Zoology: Dealing With the Wolves, Serpents & Swine in Your Life hitch-hikes off this theme.
Jesus taught that some people were wolves, some were foxes, some were goats and some were swine. In fact at one point He said,