C.S. Lewis was a fantasy author, and he has a great quote regarding his critics who worried about adults liking stories that are considered childish.
Critics who treat 'adult' as a term of approval, instead of as a merely descriptive term, cannot be adult themselves. To be concerned about being grown up, to admire the grown up because it is grown up, to blush at the suspicion of being childish; these things are the marks of childhood and adolescence. And in childhood and adolescence they are, in moderation, healthy symptoms. Young things ought to want to grow. But to carry on into middle life or even into early manhood this concern about being adult is a mark of really arrested development. When I was ten, I read fairy tales in secret and would have been ashamed if I had been found doing so. Now that I am fifty I read them openly. When I became a man I put away childish things, including the fear of childishness and the desire to be very grown up.
In searching for the context of the quote, I came across the excellent essay On Three Ways of Writing for Children. Towards the end he makes the point about how realistic fantasies can be much more dangerous than obvious fantasies.
The dangerous fantasy is always superficially realistic. The real victim of wishful reverie does not batten on the Odyssey, The Tempest, or The Worm Ouroboros: he (or she) prefers stories about millionaires, irresistible beauties, posh hotels, palm beaches and bedroom scenes—things that really might happen, that ought to happen, that would have happened if the reader had had a fair chance. For, as I say, there are two kinds of longing. The one is an askesis, a spiritual exercise, and the other is a disease.
In other words, 50 Shades of Grey represents a far more dangerous fantasy than Game of Thrones. And C.S. Lewis was saying this before the time of reality TV.