But then Heinlein gets a bit snobbish himself. He differentiates between SF and "pseudo-scientific fantasy" - which I get. Star Wars, for example, is not science fiction. The element of the "force" puts it squarely in the fantasy camp - or since it takes place in space, space opera. But he basically lumps all fantasy together as hack literature, escapist, and therefore not worthy of carrying deep thoughts. Science fiction, on the other hand, has weight.
Which is odd, since Heinlein opens the preface with the purpose of the anthology - and that is to merely entertain the reader. It's no longer "trash" (like fantasy!) but its purpose is to merely entertain? I don't get it. Anyway, here's his paragraph. I'll let you decide if his slam against fantasy holds water.
Science fiction is sometimes miscalled "escape literature," a mistake arising from a profound misconception of its nature and caused by identifying it with fantasy. Science fiction and fantasy are as different as Karl Marx and Groucho Marx. Fantasy is constructed either by denying the real world in toto or at least by making a prime basis of the story one or more admittedly false premise - fairies, talking mules, trips through the looking glass, vampires, seacoast Bohemia, Mickey Mouse. But science fiction, no matter how fantastic its content may seem, always accepts all of the real world and the entire body of human knowledge about the real world as the framework for the fictional speculation. (emphasis original)I'll have to google seacoast Bohemia*. But it seems to me that fantasy isn't necessarily escapist. It can hold 'deep thoughts' - but so what if it doesn't? Does that disqualify it from being real literature? Interesting discussion at least. Oh, and as a fan of sf and fantasy, I reject both Marx allusions. ;)
(*Ah, Shakespeare reference.)