I think, of all the stories I've addressed so far, Ender's Game, by Orson Scott Card, is more science fiction than any other. This applies from a classical-definition-of-science-fiction standpoint (it's a book about alien invasions in the future with spaceships and stuff), and from the standpoint of my own definition of science fiction, for reasons that I'll talk about in a paragraph or two. What makes Ender's Game most notable, however, is how elegantly it's able to represent the way in which science fiction's proclivity for the former enables it to clearly convey the latter.
In my opinion, Ender's Game represents one of the most comprehensive studies of morality (in particular, the moral laws that govern the use/abuse of power by authority figures) that has ever been written into fiction. However, the plot that sustains this fascinating philosophical exercise is, on its surface, utterly sophomoric. Ender Wiggin, a child of six, is inducted by the military into "Battle School," a place for children like him to be trained into the generals that will fight off a potential invasion by the "Buggers," a race of violent, insect-like aliens. As Gerald Jonas wrote in his (very positive) review of the book for the New York Times, it "sounds like the synopsis of a grade Z, made-for-television, science-fiction-rip-off movie."
And it's certainly true. But Ender's Game uses this plot to great effect. At Battle School, Ender confronts a series of games, from the virtual reality game on the school's PCs to the book's famous zero-gravity laser tag to the final command simulator. And yet, none of them are really games. Ender is too young and naïve to realize it, but every moment of his life, from his birth to his final battle against the Buggers, has been planned out. He is being manipulated constantly by the adults in his life, Colonel Graff in particular, being crafted into a weapon that the military can literally use however they please. At the novel's end, Ender completely wipes out the Buggers, but does not even learn that he has been fighting them until the final battle is over. Upon learning what he has done, Ender is wracked with overwhelming guilt, and rightfully so; he suddenly realizes that he has the blood of billions of lives on his hands.
Which has to make you wonder: To what extent, if any, is Ender responsible for the extermination of the buggers? To what extent can you hold Colonel Graff responsible? Ender's Game certainly points out the power that authority figures have. Teachers and parents have the ability to mold and shape children into any number of things. There is no doubt that parents and teachers have a responsibility to use that power, but Ender's Game makes something else clear: That power, like any other, can be used morally or immorally, for good or for evil.
There's another question, though, that is equally important in thinking about the morality of Ender's Game: The Buggers had attacked Earth twice before, and all attempts to communicate with them had failed; was their extermination even morally wrong? Is there anything that fundamentally separates them from cockroaches, or killing them from killing cockroaches? This is a particularly interesting question when viewed in the context of the recent widely-publicized comments by Stephen Hawking on this very subject. "If aliens visit us," he said, "the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans." To assess the potential validity of that statement, I would have to look towards human beings for a baseline: How would we act if we came upon an alien race? I'd like to think that we'd study them, and interact with them, but never exterminate them. But violent action against any species that is not human is incredibly easy for us to morally justify, and that gives me pause.
These are all crucial questions to be asking, in my opinion, but these sorts of questions cannot be asked except through science fiction conventions. How do you explore the implications of wiping out an intelligent but non-human race without aliens? How do you turn Ender into such powerful yet naïve weapon (and explore the questions that result from such a scenario) without the kinds of high-tech games that Ender's Game describes? I simply cannot see a way to explore these scenarios or ask these questions except through science fiction and its various conventions.
Finally, however, Ender's Game is remarkable for one reason that is completely unrelated to my conception of what science fiction should be: It had an eerily prescient view of the future. Science fiction has always made a name for itself in predicting the future of our society, many times by predicting the technology that will later be invented. The submarine in 20,000 Leagues Under the Sea did exactly that, as did the water beds that appeared in several of Robert Heinlein's books (Heinlein's detailed descriptions of water beds made them impossible to patent once someone finally invented a working one). You might say that Ender's Game accomplished this feat by describing laptop computers with advanced GUIs (called "desks" in the novel); more importantly, however, Orson Scott Card predicted how we would use them.
Ender's Game was published in 1985, long after the invention of the PC and the internet, but long before either of them had risen to prominence in society. Yet the characters in the novel use them to perform a wide array of unmistakably modern activities: web browsing, emailing, and, most importantly, blogging. Orson Scott Card was able to conceive of a future in which two children (Ender's siblings) use their parents' computer to set up and write blogs that then become enormously influential—mainly because their readers have no idea they're children. This may not seem very impressive, but consider this: The novel existed five years before the first website was created, five years before the first commercial internet service provider went into business, and ten years before the first blog was created. Orson Scott Card had a conception of the social importance of the internet far beyond that of any of his contemporaries in academics or fiction, and, quite frankly, I don't think he could have done that without science fiction either.