I work in the AI field. The fictional shows are not realistic, the authors do that for the sake of creating a powerful enemy that seems unstoppable, so the puny humans can be heroic in the eyes of the audience. (The same goes for nearly all alien invasion scenarios, but I will stick with AI.)
That answers your question; in fiction the AI cannot be benevolent and harmless, or we don't have a movie! The authors need a monster for the heroes to fight, and they "raise the stakes" by proving the monster is ruthless, irrational, remorseless and out to slaughter everyone! Women! Children! Infants! You and everyone you love, dear audience member.
On to AI: We can make distinctions to distinguish between some labels that are often conflated: Intelligence can exist without Consciousness, and we can have a Conscious Intelligence without Emotion; it does not have to want anything or fear anything (including its own death).
Intelligence is the ability to learn or discover predictive abstractions; which we call "models" of how something operates; be it gravity, water, tigers, atoms, women, Congress, electricity, the Sun, plants, fish, etc. A "predictive abstraction" is a way of translating a current state into a previous state or a future state. When you see a man looking at his phone and stepping off the curb in front of a fast-moving oncoming truck, your visceral reaction is not due to something that happened, but something you predict is about to happen, based on several models in your brain about how fast trucks can stop, how human bodies react when hit by trucks and whether he can get out of the way, etc. Your intelligence predicts all that, and concludes you are about to see something horrific, and your emotions react to that intelligence.
The more accurate, comprehensive and long-term the predictions are; the more intelligent the predictor is. But even very short term intelligence is useful; an animal that realizes the shadow that just appeared before it is a predator above or behind it can take a reflex evasive action and save its own life; even though that 'prediction' of what was about to happen was less than one second into its future. (I say reflexive to mean it wasn't a conscious decision, even though the prediction counts as 'intelligence'.)
Consciousness is very contentious and not well understood; but a useful idea is that this emerges when intelligence becomes sophisticated enough that it requires a predictive abstraction of your own self in order to predict further in the future: What you will see, are capable of doing, and how what you do will most likely influence the future. I don't think a spider is conscious when it builds a web. I think a human that examines the web, and guesses how it works in an abstract sense, and imagines herself tying strong vines into a similar pattern to trap a squirrel, has to be conscious. She has an abstract model of herself and chooses to work to bring about a future in which she has a supply of squirrels for dinner. (A non-conscious intelligence, without any abstract model of itself, may understand how a web or net works, but is incapable of imagining itself building something like it, made of vines or string.)
Once an animal does have an abstract model of itself, along with a million other abstract models about how the world works, then the intelligence can enter an infinite loop of prediction about what will happen next; and how it can influence that, or prepare for it, or avoid it, or whatever. That is us; at every waking moment we are anticipating and planning and taking action to influence the future.
However, that also demands emotion. We can anticipate the future, often with great accuracy, but if we don't care how it turns out then there is no weight given to any action! We have to want things (or the opposite, want to avoid them). Those "wants" are not always rational, and in fact most of them, if you think about it, come down to non-rational motivation: "I just want it."
For example, why do people want sex if they are certain it will be non-reproductive? It feels good. Why? It just does! The same goes for the foods we love, the pointless games we play, etc. Why do we want to live, knowing we will certainly die someday? As we follow the two-year-old's chain of questioning, asking "why?" to every answer, we end up with circular reasoning or a dead end: Eventually it is just axiomatic (a truth with no justification) that, barring very special circumstances of horrific pain, we don't want to cease existing. But that is an emotion, not a product of either intelligence or consciousness. Those both serve our emotions (and can be overridden by them), and without emotion, we do not have any 'sense' of self-preservation, no 'desire' to live, or protect ourselves from harm, or hatred or love for anything.
Oddly, it is fairly easy to develop artificial intelligence, but very difficult to create usable artificial emotions. Yet this is the mistake made by fiction writers, assuming that intelligence leads to emotions and feelings; when in real evolution, it is far more likely that emotions and feelings led to intelligence: You have to want something that can be delivered by a predictive rationality, or there is no evolutionary drive to select for predictive rationality! There has to be a reason for an animal to choose one future over an alternative; and satisfied emotions (fear, hunger, mating desire) provide the selective pressure to make ever better predictions.
In AI, we humans provide that selective pressure: We instruct the AI to prefer better accuracy over less accuracy; because we want, say, investments in the stock market that will pay off, because we want wealth. Or for a less crass example, we want an accurate prediction of how a medicine will behave in the body, because we want to save patient's lives and alleviate their illness or disability.
AI is useful, but as just intelligence, it is benign. It may make very accurate predictions of the future, for humans to exploit (and of course humans can be very evil and consumed by emotions they cannot control). But without a sense of self (consciousness) the AI is just a prediction engine. Humans must decide what makes a solution better, and their criterion should logically prohibit killing everyone.
A Conscious AI is similar: A robot could be conscious, able to plan its own future and actions (whether right now or years in the future), but it doesn't have to have emotions. I don't think Asimov's laws are that useful, but we can say a robot's motivations is to, say, provide care for patients within certain boundaries of action; otherwise it calls for doctor (like a nurse in a hospital). Really all of what a surgeon does is rational and motivated by restoring function, reducing harm, keeping the patient alive and (eventually) with minimal pain or disability. A conscious robot could do that, without emotion.
For a conscious AI, I can't imagine why we would give it any emotional states at all. It would not fear being shut down or "killed", it would not conclude that its best service is to kill everyone. Without a human-provided goal, it would sit and cycle forever, never getting bored or frustrated with inaction (because boredom and frustration are human emotions).
That is all fiction for the point of creating a daunting monster; nothing more. If an AI kills 99% of humanity, it will be because some insane human wanted that, and told the AI to find a way to do it.
In reality; a sufficiently complex AI, perhaps with consciousness so it can conceive of and plan and execute safe experiments, could be instructed to find an affordable, scalable and safe clean energy solution, which would directly or indirectly solve nearly all the problems of humanity.
But if you are writing an action flick, that AI is not much of a villain, is it?
