Years ago, I owned a bookstore in Waynesville, North Carolina, where we sold used and new books, and a healthy collection of children’s literature. One summer afternoon, a woman accompanied by two adolescent grandchildren entered the store. While the kids browsed the shelves, the grandmother and I visited at the checkout desk. At one point during our cordial conversation, she looked at her grandchildren, both of whom were absorbed in books, smiled, and said, “You know, I don’t really care what they’re reading as long as they’re reading.” Only the desire for a sale—like most independent booksellers, I always needed cash—prevented my reply: “That’s like saying, ‘I don’t care what they’re eating as long as they’re eating.’” What we put into our brains is just as crucial to our health as what we put into our bodies. An example: Once at Waynesville’s public library, I was standing behind a young …