From a selection of science fiction classics I'm familiar with...
Which is most worrisome? That is, either most likely to happen, or so bad as to be especially troublesome?
I've chosen classics of science fiction I hope you are (mostly) familiar with, but it's the nature of this sort of poll that popularity is mixed in with the question of which vision presented is most frightening. You might find one you haven't read the most frightening if you had the chance.
Still, most of you are likely to be a little familiar a book such as "1984", and if you like sci fi classics, you'll probably be familiar with them all to some degree.
Note: Further reading suggestions within the genre welcome.
These Books:
These books are mostly about overtly strong, controlling cultures. There is generally a mix between the physical power the culture uses to control and the complicity of the individual in the culture. All can be seen as cautionary tales (although it's hard to tell where that stops and pessimistic declaration begins), and lessons about propaganda and lying to oneself.
In 1984 the people are not watched all the time ala the popular cliché of big brother, not quite. No, everyone is required to have cameras in their home all right, but you do not know if the camera is on, when it is on, if it ever goes on. That threat is an important part of the recipe, but "doublethink" and public complicity is the real villain in 1984.
Many of the writers seem aware that the power is with the numbers... the only defeat of the people comes from subduing the people (the people's subduction?).
In "A Brave New World" we have a culture that is content, it's a socioscientific government in which the people are very complicit because they are made effectively happy with drugs and pleasures. Creativity is stifled, except for a shallow type of creativity (correct my poor memory please if nec.) perhaps, that which provides an instant gratification. One could call the pleasures allowed purely base, and it's a negative vision with a protagonist that emphasizes this but ambiguously.
The change in culture seen in the main part of The Time Machine is more complete because evolution has entered into the equation and the human race has changed radically. A Faustian bargain has been taken by the ruling class and has lead to a situation where they are hunted and helpless, albeit still pampered, living in gardens, taken care of by their underground living keepers. Who is more free or more despicable is a question defied and denied in this classic, and optimism isn't allowed if the future is final and the system then biologically required. Of course, there is hope for us in the real world still.
Even more final pessimism exists in "On The Beach", which is about the last days of the last people on Earth dying after a nuclear holocaust. It's not a happy ending. This option is really one that lets war into the poll... it is the idea that mankind will destroy itself in war, that the type of culture, good or bad, just or unjust, might just be a secondary question if we destroy ourselves anyway.
Fahrenheit 451 presents another situation where people are complicit in the prohibition of books, the peer pressure, or peer oppression, is evident. Their fear of books is shared and their culture, which they are largely content with is harsh and ignorant as a result. This is not to say the norms are not enforced on those that do no not comply, of course they are and a protagonist that cannot fit in is common in those of these books to which this pertains.
"Futurological Congress" from 1971 involves a future in which the governments release cocktails of drugs into the water and air, etc, so that the people are constantly drugged into hallucinations. The world is crowded, polluted, people eat from traughs, but they are convinced they live in an ideal utopia, and that's what you see around you unless you counteract the drugs. The drugs can give you education, attitudes, and seemingly any state of mind.
These books are books about the individual and society, and in the worlds presented the individual is dealt with as a chronic affliction, as an outsider, or as simply irrelevant.
Honorable Mention: "Memoirs Found in a Bathtub" (Lem) not present because it doesn't quite fit that list though I think it's on topic. It's really about a NORAD type installation after sealing itself off for an indeterminate time (generations?) and becoming it's own enemy, a culture of paranoia with nothing left but the paranoia to keep it going. It's about culture but not really a general population. Plus it's more allegorically absurd with few literal interpretations of events. "Futurological Congress" has similar absurd elements, but does offer a functional description of a technologically subdued populace, willing because it's good enough to feel good. It is a picture of a capitalistic culture that has sought out a utilitarian dream of satisfaction maximization, reacting therefore to problems after they can only be mitigated (i.e. after you pollute the world, drug yourself out of noticing it.
Variant interpretations are also welcome.