The stories of Jesus always imparted knowledge and further understanding of godly living or a furtherance of His Kingdom. If not, neither should we. Never should God's Word be violated in the name of fiction. Much of what is labeled Christian fiction could never be read out loud to Jesus. Much of today's Christian fiction is aimed at our carnal nature, and the author's desire to make a profit at whatever the cost.
Evil can be incredibly deceptive.
In a nonfiction book a reader is more alert to any false teaching. A nonfiction book has a straightforward goal, and one can easily debate wrong arguments. However, a storyteller weaves his philosophy in and through the medium of a good story. Undiscerning readers are not aware of all the false truths slipped into the story. Fiction can be a dangerous thing.