The gaming mindset is completely different from the reading or watching a movie mindset. Your brain is behaving differently, and also expecting a different kind of stimulation. To analyze the content and effects of one medium by the rules and parameters of the other is a big mistake. And to analyze any of those mediums as if it were reality, your mental and ideological reality to boot, is criminal.
In a movie or book, when a protagonist fights a person and ends up killing it, the killing itself is meaningful and (usually, especially in books) not exchangeable. It is not a proxy for another thing, like enjoyment when you overcome some obstacle. If you remove that action, the story changes. If you change some element of that action, the why, the how or when, the story changes. You, as a passive observer without any goal inside the fantasy world you are experiencing, merely follow what the creator intended and you enjoy (or not) the narration and story. Now, if I kill an enemy in a video game, this hardly matters in any aspect. Why did I “kill” them? Because they are in my path towards finishing the game; the game protagonist may have some sort of “motivation”, but you don’t really have to believe it. On the other hand, if you don’t find the book or movie plot believable, it’s unlikely you will finish the thing.
I once began to count how many enemies I was killing while playing Max Payne 2. I was around the second half of the second chapter (it has three), and I already had an astounding 248 dead people behind me. Let’s assume the game has 500 enemies. Why are those 500 guys there? They are a challenge, and nothing more. They don’t add much to the plot or story (I said much, not anything), which you can experience reading the comic strips and a few cutscenes. Any other medium with a description (using words or images) for 500 individuals being killed would be insufferably tedious and boring, but those enemies aren’t there to be described, experienced, empathized or anything else. They exist to test you. When a “cultural critic” says that violence in video games is out of control, he could very well be saying that the targets in a shooting gallery are out of control because there are too many of them or they are becoming more realistic with each passing day.
A video game creates an artificial problem that needs to be solved by its own rules. If the game is good, the problem will be challenging, stimulating and not just a repetitive work. For your brain, it does not matter that much how the problem is represented, what matters is how exciting it is to play and solve it. Is it killing the enemies, sneaking past them, talking to them, peeing on them? Who cares. Killing is, in fact, a designing choice that makes the whole game easier to create since once the obstacle has been removed, it is removed forever. It simplifies things as is a gaming tradition, and considering that most games are about fights, adventures and that sort of things, it’s a reasonable game device.The idea that such games make a deep philosophical or ethical point about it, or that you SHOULD make it, is pure sophistry and academese bullshit.

Movie action shootouts are similar in that aspect since enemies are there just to “die”, but games are even less “violent” since the gaming part is emphasized at the expense of passively watching people being blown up. In a movie, the sound, blood, and other characteristics are necessary to create the specific sensory experience (which, by the way, is still not realistically violent in almost any way). On the other hand, in games, gameplay (if the game is good and doesn’t try to be “Hoolywood”) is emphasized, and what matters are your reflexes, number of weapons or tools at your disposal, map design, etc (I’m assuming a basic first-person shooter experience). Not surprisingly, good translations between movies, books, and video games are few and far in between. Imagine yourself trying to make a good book from a very detailed shooting gallery with some in-game lore and you get the idea.
Is a shooting gallery violent? Because that’s what “violent” video games are. A moving, intelligent, sometimes adaptive shooting gallery, but it’s just a test for your abilities. Change the target for a moving tomato and people will still play it, perhaps even more since now it’s more ridiculous than before.

Source: The Simpsons Doom 1 & 2 Total Conversion Wad.
Not understanding this is not understanding the core characteristic that defines playing: abstraction from the real world and its consequences, formal rules, a test for your abilities, and the possibility of winning and losing. The goals may be fixed, open or even self-created (like in a sandbox simulator), but there are goals so you can feel a sense of accomplishment, and that requires the possibility of failure. When was the last time you failed watching a movie, reading a book or contemplating a painting, and -therefore- you could not continue? You can get stuck playing a Sherlock Holmes video game because you don’t succeed doing the correct deductions, but not while watching a movie or reading a book about the greatest detective.
Not surprisingly, the most violent disturbing scenes in video games are, in fact, not games at all but movies or even good old-fashioned text. I’m talking about cutscenes and forced dialogue. By taking away your playing ability, your freedom of choice and your agency, the game stops being a game and becomes a passive exercise in observation and reading. In those scenes, they can force-feed you all the violence, message, propaganda (or even art) they want, and other things that would have looked a bit ridiculous in actual gameplay.
For example, this is how JC Denton, the protagonist from the original Deus Ex deals with an antagonist. For those who haven’t played the game, that’s only one of the many things you can do in that scene (it’s not even necessary to kill her… or even to be there), and it’s not scripted or anything. In fact, it’s possible the game designers didn’t even thought about that one. We are talking here about emergent gameplay, about how the player uses his creativity and the freedom the game gives him to carve out his own way to solve problems.
And this is how Adam Jensen, the protagonist from Deus Ex: Human Revolution deals with another Chinese antagonists (the game is a prequel, set 30 years before the original).
As you can see, it’s a movie, not gameplay. The first is an example of something ONLY games can do; the second is a scene that has to be judged by its own merits as a scene inside a story, but it could have been a movie or a book. Another example, this cutscene from the Witcher 2. It’s an attempted rape.
You do nothing, they force you to see it as the game designers intended. Drama, tension, and violence can be expressed with cutscenes, but with gameplay? How would you even express that in game mechanics? If you don’t intervene… what, they rape her and you can hear it from the other side of the building? Not surprisingly, old video games were more tongue-in-cheek and didn’t take themselves too seriously since it’s difficult to do that in a pure game. After all, gaming is abstracting yourself from reality.
This does not mean they were comical; Thief is an example of very dark game that still could be fun and didn’t have that emo gravitas modern games have, like the latest Thief 4. Compare the two garretts:
To create drama and tension (or force-feed a political message) you have to take the controller off the player hands, otherwise he may just ignore you and whatever you are trying to explain. In other words, to become more than games, games should stop being games at all.
Modern games, attempting to make the experience mature and deep (in most situations that just means being edgy), have only made the games less, well, games. Sometimes the attempt at being mature is just ridiculous since they want you the believe you are experiencing something real with choices and consequences when you are just hacking virtual avatars (hundreds of them) with your virtual sword. Also, they are constantly taking the game from your hands, streamlining your experience, force-feeding you emotions and how you should feel about what you are seeing.

Source: Some Call of Duty game I’ve already forgotten. Modern something or other.
The greatest video games have avoided this trap in two ways: integrating history in the game/map design and in non-intrusive text or logs that explain what is happening. Or completely separate history from gameplay, explaining the former in mission briefings or a few cutscenes between missions. With the exception of roleplaying games with high quantities of dialogue (since, sometimes, that works as gameplay), most of the “violent” or disturbing material in video games will be found in those segments or extras, not so much in the proper gameplay. That should not be THATsurprising, though, since literature and movies have the greatest evocative power. However, realizing that requires thinking, so most moralist won’t see it and will keep hammering about guns, explosions, guts and the occasional lady with big breasts.
Still, let’s assume you really need to write a paper or editorial about video game violence, and you just don’t care about anything I just said. Those stupid gamers hardly ever defend themselves so who cares. Perhaps you realize violence inside the proper game is difficult, but you still want your readers to believe there is some spill-over effect into the world (no, not really). Well, now, to understand violence thanks to video games you must first be able to differentiate between aggression, frustration, and violence. If you can’t, you should not be talking about this issue (assuming you care about truth).
Video games, like all human activities, can provoke frustration, which can lead to anger, but that does not depend on the graphic representation or gore levels of the game. The most frustrating and rage-inducing games I’ve ever played were old-school adventure games. I think I could have murdered someone after hours playing Monkey Island 2. Why? Because in those games you get “stuck” and can’t continue. Similarly, modern military shooters are rage-inducing not because they represent war (yeah, sure) but because they remove so many things from your hands that you are in some sort of virtual rat maze and dying feels like an unfair or even arbitrary punishment. On the other hand, a game like Unreal Tournament can become something close to a Zen experience since it has a fine gradation of difficulty levels that adjust almost perfectly to your playing style and ability. There is considerable freedom in the game, and there is also constant feedback for everything you do and realizing why you failed is always possible.

Frustration, therefore, appears in those games that have strong yes/no stuck points or, simply, aren’t well designed and have terrible encounters, uneven boss-fights, or horrendous difficulty curves. Some adventures games are the most evident culprits of the first kind since you can only continue playing once you have combined an specific item with another specific item, and sometimes the combination is quite arbitrary. This is important since there is, still, that strange conception about how aggressive player behavior or negative emotional states require violent representations, as if your mind reacted to them. No, you only need to get frustrated, and it could be while playing minesweeper for all we know. If the game has a correct flow, it could be the most violent, gory and disgusting thing ever imagined and you could still play it as a relaxing experience. If your kid is screaming at the screen, it may be that he plays shitty games or perhaps you need to smack him a little.

Source: Brutal Doom http://vgjunk.tumblr.com/post/72235704540/brutal-doom
Also, it should me noted that moderns gamers have less tolerance to frustration than older gamers. In any event, then you also have online games, competition tournaments, etc. those may provoke frustration for a certain type of people, and certainly aggression if the stakes are high. But almost the same happens in any competitive experience so there is nothing very special about video games in that department.
There is also a difference between frustration and aggressivity/competitivity as human emotions or feelings. Frustration comes from “immobile” obstacles, non-sentient entities (trying to repair a computer that refuses to work) or things designed, created or produced by people you can’t punch directly (hence Internet frustration in on-line conversations you can’t control). You also experience it when you believe you are being unfairly/arbitrarily punished for something you actually did well (or so you believe), or that your problems are not your own fault. Simple aggression requires a more face-to-face approach and does not need a “I’m losing or not accomplishing anything” mentality since it’s not a “reaction” to something. One can be aggressive just to win, even before you begin playing. In that sense, aggression is not a dangerous or hostile thing by itself.
That aggression I mentioned is another word for competitive mindset, and it seems to be a male thing, linked with testosterone, status fights and “winning” mentality. It should be noted that this aggression, along with competition and testosterone, are not directly linked to physical violence since you only need to compete to feel it. ANY kind of competition will do, even if it’s a mental sport like chess.
“Competition among chess players is a step closer to normal social competition because it does not require physical struggle, and it is the arena for tests of the T mechanism we have reported here. We find that winners of chess tournaments show higher T levels than do losers. Also, in certain circumstances, competitors show rises in T before their games, as if in preparation for the contest. These results generally support recent theories about the role of T in the allocation of status ranks.”
From the abstract of:
As anything else when something is at stake, even if just reputation, aggressivity is possible, and certainly hostility, but… violence? There is hostility in on-line gaming communities, but if you dig deep enough, you’ll soon see that the real causes are as new as they were in the Illiad: pride, hubris, hurt-feelings, personal dramas, etcetera. In my experience in video game forums, talking about video games actually reduces the level of vitriol in any conversation. If it degenerates into something worse you can be sure there is some previous personal drama, or that someone is trying to move the issue from the hobby to other subjects like politics, identity issues, or -simply- the lack of intelligence of the poster.
Amusingly, there are certain people who believe video games have the power to make people better, and their plan to accomplish that isn’t something as revolutionary as let people have fun but to insert politics, identity issues, and charged subjects into the game experience. That would be like trying to solve aggression in soccer by injecting nationalism and ideology in it. It’s still amazing how many people truly believe that politics, which in modern discourses is linked to group identity, collective narcissism, and self-esteem, can make the world a better place. I’d recommend a worldwide Unreal Tournament championship with scantily clad women as cheerleaders, but what the hell do I know. I’d probably be reinforcing misogyny, rape culture and imperialism. Or something.