The trajectory of sci-fi narratives occasionally transcends conventions, simply because they embark on a journey with minimum knowledge of the future. In the course of events that follow, these stories take the viewer into their own mind, exposing them to the radicalism that lies in reinventing the world; consequently break the barriers that separate sociocultural norms.
One of the most important features of the sci-fi movie, although not present in every single example of the genre, is its antagonist — a force that threatens to shift the tide and undo the delicate balance that holds their universe together. Sometimes, however, there is a certain lack of cinematic translation (intentional or otherwise) that makes their motivations ambiguous. In other words, there are villains for whom redemption is justified.
Redeemable: Roy Batty — Blade Runner (1982)
Roy Batty spends an inordinate amount of time musing on the philosophical ramifications of his existence, at least whenever he isn't trying to kill those responsible for his creation. Further, he takes Deckard on a strange tour of his mind, forcing the Blade Runner to experience fear and misery.
However, when he observes one of his "dead" comrades, he starts to cry, showing that he does have emotions coded into his algorithm. Interestingly, though, he saves his opponent's life at the end, right before he is automatically deactivated.
Too Evil: The Xenomorph — Alien (1979)
Although the origins of the species remain shrouded in ambiguity, there is no doubt that the Xenmorph's viciousness knows no bounds. They are evolutionarily designed, either by their creator or by nature, to stalk, hunt, and murder their quarry by any means necessary.
Further, they exist as a hierarchical Hive Mind, with a vastly powerful Queen Mother at the top — their only aim is to seek out new planets to "harvest", without a single hint of compassion or doubt in their own decisions. There is no saving the Xenomorph.
Redeemable: The Thing — The Thing (1982)
The Thing is an unknown extraterrestrial creature discovered in Antarctica. It works like a gruesome parasite, "assimilating" its poor victims in agonizing ways, before being able to transform themselves according to the DNA code imbibed.
As violent as their methods seem, The Thing is simply another organism intent on surviving, like any other form of life. They do not actively despise anyone or anything, but only do as their genetics tell them.
Too Evil: Immortan Joe — Mad Max: Fury Road (2015)
Immortan Joe is a classic tyrant, but where modern-day dictators stockpile money and land, he hoards something far more precious in the post-apocalyptic wasteland: water. He refuses to give his "people" more than a few drops at a time and simultaneously subjects his own warriors to deceitful visions of a heroic afterlife while sending them to their deaths.
Joe uses human beings for his own ends and exhibits nothing but creepy and abusive tendencies.
Redeemable: Tetsuo Shima — Akira (1988)
Tetsuo Shima has spent his entire life under his best friend's more charismatic shadow, for which he resents Kaneda enormously. This misplaced animosity is derived from his own perceived lack of inner strength and confidence, and he looks at his pal's attempts to bond with him as a relationship between a master and servant.
Tetsuo has an apparent change of heart once he gains Esper-like abilities and accidentally finds himself being consumed by his own body. He begs Kaneda to save him, but any rescue endeavors meet an unfortunate failure.
Too Evil: Hal-9000 — 2001: A Space Odyssey (1968)
It can be argued, with adequate evidence, that Hal-9000 is a victim of circumstance, that the hostility he displays is due to his own internal strife — the impossibility of choosing his specialized task in favor of his global directive.
Still, the cold-blooded manner in which he intentionally causes the deaths of Poole (and the astronauts in suspended animation), before dispassionately rejecting Bowman from coming back into the safety of the shuttle is unnerving, to say the least. Hal-9000's inscrutable behavior has obtained him a position among the American Film Institute's best villains of all time. Hal did achieve some redemption eventually, though not in Kubrick's movie. The AI returned in Peter Hyams' sequel, 2010: The Year We Make Contact, in which some of his behavior is explained.
Redeemable: Ava — Ex Machina (2014)
Ava is created by a genius, uber-wealthy programmer within the depths of his enormous mansion, where he subjects her and his other newborn AI to unnecessary humiliation (including sexual abuse.) After this treatment, it's not surprising that his greatest invention would violently turn on him.
It's strange that Ava also left Caleb to die before disappearing into the world, but no consciousness appreciates being kept under lock and key, not to mention experimented on. Does Ava deserve to suffer simply because she's made of silicon and graphene instead of flesh and blood?
Too Evil: Agent Smith — The Matrix (1999)
At first, Agent Smith works on behalf of the Matrix, but his "death" at Neo's hands sparks something of an individualist inferno in him. He has always found humanity abhorrent and worthless, and his rebirth allows him to take his personal vision into reality.
He's stopped, of course, when the Deus Ex Machina sends Neo back to defeat him, but if he had been unrestrained, the entire world, both people and machine, would have been decimated. Sinister viruses are meant to be expunged from the body, just like Agent Smith is at the end.
Redeemable: Wilford — Snowpiercer (2013)
Wilford claims to have been the brains behind the whole Snowpiecer idea, while simultaneously running a mega-corporation named after himself. He is callous enough to force children into a horrifying (and, presumably, short-lived) existence as replacement workers for the Engine.
What's worse is that he forcibly separates them from their parents, but never from the wealthier cars, indicating his belief in a class system. However, what matters is that he has somehow kept the last remnants of humanity alive for 17 years, and that drive and ingenuity show at least some faintly redeemable characteristics.
Too Evil: Human Beings — Avatar (2009)
The Na'vi are as intelligent, courageous, honorable, and compassionate as human beings can be, except all the time and without fail. People, on the other hand, have completely annihilated their own world, forcing it beyond its capacity to maintain life and are now preying on innocent aliens who had done them no harm.
Capitalism thrives in all its brutal glory, among the stars as it did on Earth, and these people will stop at nothing to obtain Unobtainium, even if it means exterminating a living planet. The fact that humans are also on the side of justice does nothing to mitigate the malevolence of their kind. Perhaps they'll behave better in the sequels.