Ursula Le Guin, from "Why Are Americans Afraid of Dragons?"

I don't agree with everything she says about art and sterility in this essay, but as a defense of Fantasy as a genre, this is a pretty interesting approach. To give you some sense of context for the passage from The Language of the Night that I'm about to post, she's theorizing that something must happen in childhood that cultivates a rejection of Sf (and in particular, Fantasy) in people.

"So I arrive at my personal defense of the uses of the imagination, especially in fiction, and most especially in fairy tale, legend, fantasy, science fiction, and the rest of the lunatic fringe. I believe that maturity is not an outgrowing, but a growing up: that an adult is not a dead child, but a child who survived. I believe that all the best faculties of a mature human being exist in the child, and that if these faculties are encouraged in youth they will act well and wisely in the adult, but if they are repressed and denied in the child they will stunt and cripple the adult personality. And finally, I believe that one of the most deeply human, and humane, of these faculties is the power of imagination: so that it is our pleasant duty, as librarians, or teachers, or parents, or writers, or simply as grownups, to encourage that faculty of imagination in our children, to encourage it to grow freely, to flourish like the green bay tree, by giving it the best, absolutely the best and purest, nourishment that it can absorb. And never, under any circumstances, to squelch it, or sneer at it, or imply that it is childish, or unmanly, or untrue.

For fantasy is true, of course. It isn't factual, but it is true. Children know that. Adults know it too, and that is precisely why many of them are afraid of fantasy. They known that its truth challenges, even threatens, all that is false, all that is phony, unnecessary, and trial in the life they have let themselves be forced into living. They are afraid of dragons, because they are afraid of freedom.

So I believe that we should trust our children. Normal children do not confuse reality and fantasy -- they confuse them much less often that we adults do (as a a certain fantasist pointed out in a story called "The Emperor's New Clothes"). Children know perfectly well that unicorns aren't real, but they also know that books about unicorns, ift hey are good books, are true books. All too often, that's more than Mummy and Daddy know; for, in denying their childhood, the adults have denies half their knowledge, and are left with the sad, sterile little fact: "Unicorns aren't real." And that fact is one that never got anybody anywhere (except in the story "The Unicorn in the Garden," by another great fantasist, in which it is shown that a devotion to the unreality of unicorns may get you straight into the loony bin). It is by such statements as, "Once  upon a time there was a dragon," or "In a hole in the ground there lived a hobbit" -- it is by such beautiful non-facts that we fantastic human beings may arrive, in our peculiar fashion, at the truth (44-45)."

-Ursula Le Guin, "Why Are Americans Afraid of Dragons?" (1974)