The following quotes are from a post that is actually about Science Fiction as an MMORPG, but it has some discussion which definitely applies to written fiction.
In my view, all the most-popular SF (Fiction or Fantasy, you choose) like Star Trek, Star Wars, SG, BG, etc. More closely resemble fantasy than SF.
In these, you’ll find all the character-centricity you need to make a compelling story. The setting (the technology) is incidental to the story rather than the focus. When you start throwing in goofy aliens with weird “powers” (or Chicago mobsters, or Nazis, or mutants, or ….) you are starting to get awfully close to reskinning fantasy in space. And honestly, thats not necessarily bad.
Here, where SF can stand for Science Fantasy (an obvious oxymoron if I’ve ever seen one), I think a more appropriate SF would be: Space Fantasy (as the other can be called “High Fantasy” – a term I’ve heard before, which I believe applies to things like A Game Of Thrones). It takes place in Space, and it’s basically a Fantasy.
Too often pure SF is more about the idea and not the character, or if about the character, it has a dependency on a technological element that is both critical to the story and too susceptible to being over taken by our headlong technological rush into the future potentially rendering the dramatic heart of the story irrelevant or to quote Wil, downright silly. Its much easier to keep our disbelief suspended when we’re talking about the Force in another galaxy than to disregard what have become now-glaring factual inaccuracies (or implausibilities) in light of scientific advance. FTL travel or the gravity problem anyone?
And that is why most laypeople (I believe) just call it SciFi no matter what narrower definition could possibly be applied. It’s not technically Science Fiction, the narrow definers argue, but it certainly is Fiction. And the term SciFi differentiates it from pretty much every other sort of fiction there is. It’s not (usually) horror, mystery, romance, fantasy, chick lit, or anything else. Sure, it can be a mix of SciFi with any other genre, but it’s still going to be distinguished as SciFi.
I accepted this concept starting with Neal Stephenson’s lecture at Gresham College in which he basically asserts that Science Fiction doesn’t really need to be narrowed down as a genre since (these days) everything that is not another genre is Science Fiction. It’s not a hard and fast fact, but more a byproduct of the way we are currently producing content. Science Fiction has become so mainstream that it, as a genre, can encompass just about everything that isn’t cordoned off by another group.