If I had to describe what sicence fiction is in a short sentence, I would say "it's the literature of ideas". What the SF author does is take one current trend or one possible future evolution and imagine what will happen if that trend continues in the long run, or if that evolution comes to happen. As such, SF is often about social and human interactions, rather than technology and gadgets. The "redeeming social value" of SF consists of predicting the ultimate consequences for society brougth by continuous technological or sociological change.
True science fiction should never be confused with either "space opera", fantasy, or "sci-fi". To understand what each one of these are, let's see some examples.
Space opera is, for instance, the "Star Wars" series of films. Those are based on visual effects, the setting in distant or future places is purely incidental, a gimmick to justify the Fx.
Fantasy is something like J.R.R. Tolkien's books or the films based on them. Fantasy uses beings like elves, gremlins, trolls, etc. There are magic powers, based on supernatural forces. The "Star Wars" films I mentioned above also have some elements of fantasy, such as the "force" used by the jedi knights.
"Sci-Fi" is just a despicable abomination, it's an attempt to create science fiction done by amateurs who should at least try to learn the basics before they start working. An example of the worst kind of sci-fi is the "Matrix" film with that laughable "taking energy from humans" thing. The Matrix is an example of what happens when you give too much money to people with too little brains.
As a counter-example, showing how a good work can be done from the same basic idea, take the film "The Thirteenth Floor". It's based on, roughly, the same basic idea as "The Matrix"; it was done with much less money, so it doesn't have all those Fx, but it's infinitely better. In this film, a company is doing research in virtual reality and has created a simulated universe, so perfect that the simulated beings in it are conscious. The whole film is basically a study of ethics, of which restraints a scientist must use since his creations acquired conscience and the capacity to make decisions, to suffer and to be happy, etc.
In conclusion, I would say that true Science Fiction is a basic necessity of Humanity, it's an applied branch of philosophy and ethics that tries to prevent the possible ill-effects of technological and social evolution.
Fantasy and space opera are light entertainment, they are creative arts that distract the mind. Even if they do not have the same serious transcendence as science fiction, they are also neccessary for humans, because our brain needs some rest from time to time.
On the other hand, sci-fi such as "The Matrix" or "The China Syndrome" has no value at all, it's worse than the worst kind of pornography. It's so bad because it's based on lies, it disguises bullshit as "science and technology". By creating a negative image around science and technology it works against the tools that we have against suffering and poverty. The subliminal effect of such a negative image must not be ignored, we have in many countries now laws restricting the use of nuclear energy or genetically improved crops, for instance. Such laws, promulgated solely because of histerical propaganda without any basis on reality, are controbuting to keep millions of people in sub-human conditions.
