Robert Heinlein, author of Stranger in a Strange Land, said: “Kids want tough books, chewy books — not pap.”
He called his books “speculative fiction” rather than “science fiction,” in the tradition of Jules Verne and H.G. Wells. He tried to write about events that could actually happen, taking into consideration everything we know about the natural laws of the universe. He wrote about things like atomic bombs, cloning, and gay marriage years before they became realities.
He also said, “Being intelligent is not a felony. But most societies evaluate it as at least a misdemeanor.”