Satan's Harvest

This is one of the classic paranormal books about the work of Ed and Lorraine Warren. I read it when it first came out, and have returned to it several times since then. I would have preferred that this latest edition include an update on the people involved, but it didn't. In any case, it is a fascinating look into paranormal investigation. I have one question that I can never answer. If I don't believe, as I rationally tell myself, why do these types of books frighten me?