The video is just a few minutes long, but it may be the most important game footage to be seen this year. It's a bootleg of a mission from Modern Warfare 2, the first-person shooter certain to be the winter's biggest-selling game. It shows the player joining Russian terrorists on a rampage through an airport; civilians are gunned down as armed men run through the departures lounge, and it's evident the player is firing too. In one alarming moment someone is shown dragging an injured person across the concourse – the player kills them both.

Released on to the internet last week, the blurry footage has already provoked criticism, with a Mirror headline proclaiming: "Leaked level makes light of terrorist atrocities". Many see in it harrowing evocations of last year's Mumbai terror attacks in which more than 170 people were killed. For a while, it wasn't clear whether the sequence was genuine, but Activision has released a statement confirming its authenticity: "The leaked footage was taken from a copy of game that was obtained illegally and is not representative of the overall gameplay experience in Modern Warfare 2. Infinity Ward's Modern Warfare 2 features a deep and gripping storyline in which players face off against a terrorist threat dedicated to bringing the world to the brink of collapse … The scene is designed to evoke the atrocities of terrorism. At the beginning of the game, players encounter a mandatory 'checkpoint' in which they are warned that an upcoming segment may contain disturbing elements, and they can choose not to engage in the gameplay that involves this scene."

So what should we make of all this? To some commentators, video games by their very nature "make light" of anything they portray. This is partially about semantics – the interpretation of the word "game" as something fundamentally frivolous. Partly, too, it is about the legacy of video games as a pastime for children, not for adults.

Interactivity itself brings in complex moral questions. If a movie were to depict a terrorist outrage, the viewer takes no active part. But in a videogame, you're engaged and complicit. The participation is the entertainment, and that's always going to be problematic. Activision's argument about seeking to portray the depths of the terrorist cell's immorality in order to stir the player's emotions is sound to a point – it's an established narrative device. But is it necessary for the player to throw grenades? And wouldn't similar revulsion be elicited if the player were placed into the shoes of one of the victims? This would, after all, reflect the wonderful opening sequence to the original Modern Warfare, in which the player takes on the perspective of a prisoner who is bundled into a car and later executed.

What we're robbed of when viewing this illicitly posted footage is what happens before and afterwards, the exact nature of the scene, and the authenticity of the player's involvement. The problem is, context can easily become an excuse to portray wanton violence. In the PlayStation title Driver, for example, the gamer is ostensibly controlling an undercover policeman posing as a criminal, but this backstory is immaterial to the game action, which involves stealing cars, smashing other vehicles out of the way – and having lots of fun in the process. That's a very different game, and a very different circumstance, but it's an example of how the framework can be bent to suit the core game dynamic.

I'm also unsure about Activision's claim that the scene can be skipped. It's something of a cop-out rather than a pertinent justification. The point is, it's there – the developers put it there. It is an intended element of the experience.

Responsibility is the deciding factor. Infinity Ward is an excellent developer, using narrative in a mature and sophisticated way. Witness the nuclear explosion sequence and the apparent death of Captain Price in Modern Warfare; moments of sheer emotional resonance that would have been fumbled or avoided by most studios. Both moments work perfectly within the game's depiction of a desperate global battle. I'm certain that will be the case here.

That is why this blurry, inconclusive footage is so important. The scene portrayed may well represent a statement of intent: this is what games are capable of now – unsettling us with their powerful imagery, backing us into difficult situations, toying with our moral certainties. It is an 18 certificate game. We must be trusted to test ourselves against this.