If I pick up a book with spaceships on the cover I want spaceships. If I see one with dragons I want there to be dragons inside the book. Proper labeling. Ethical labeling. I don't want to open up my cornflakes and find that they're full of pebbles... You need to respect the reader enough not to call it something it isn't.
Well right now I'm very fascinated with 1920s Berlin. I mean probably the more interesting thing would be to go to the beginning of civilization or precivilization - like polytheistic times. It would be interesting to see what came before modern religion and culture - what circumstances created the environment or the need for it.