I wanted to post this as a comment, as that would make for a much better-flowing back and forth synthesis of our points, but instead Google decided I'm not allowed to do that. Ah, the wonders of technology!
So, in reply to Aethelstan's point about Iron Man:
Sure, however, while Iron Man rapidly ditches Afghanistan for the US of A, the beginning of the film is quite clearly fuelled - at least in part - by a revenge fantasy, as is the segment where Stark, in his finalised battlesuit, flies into a hostage situation and kills all the terrorists for no loss of friendly life.It's absolutely true that the update abandons Vietnam and Those Goddamn Commies, at least in part (depending on what you think of Iron Man 2), but then it had to; SF must shine a light on its own, contemporary society. That said, you've touched on two interesting themes which I will return to. Racism and propaganda.
And now I return you to your regular schedule.
Before I go on to discuss the Analytical strand of SF, and before I discuss anything else, I need to provide you all with a definition, which I foolishly forgot to do earlier. What is SF? For me, SF is a very broad church. It encompasses everything from pulp epics like Star Wars through to the time-travelling alternate history Guns Of The South by Harry Turtledove, via Frankenstein and quieter, subtler works like Survivors and Threads or the bizzare surrealism of Emma Peel and Mr Steed in The Avengers.
But why is this? Surely there are core, identifiable elements that make, say, The Man In The High Castle by P.K. Dick an SF work, and, say, Turtledove's (mediocre) Hitler's War not, despite both being alternate history novels. And indeed there are; Hitler's War remains entirely rooted in reality, with a single point of divergence - Sanjurjo's survival - from which branches a whole new timeline. There are no leaps in technology, no meddlers from the future.
On the contrary, High Castle has an Axis victory in WW2, followed by spaceships, the draining of the Mediterranean, colonies on Mars and the Moon... quite clearly an SF work. The difference at first appears clear: technology. But, is that all it is? Rayguns and aliens, nanomachines and spacecraft? I would argue no, but I am currently out of time; so I shall conclude my definition more neatly later.
In the meantime, please, add your own ideas and I will respond.