You should also keep in mind that there are legitimate reasons why games are so violent, and it isn't just because "Hurr shooting things is fun."
When videogames first popped onto the pop culture radar around the late 70's and early 80's, computers were a lot simpler than they are now. Way, way simpler. We couldn't simulate vast social networks or allow users to upload user-created content onto a webserver for all to see. Hell, we couldn't save your high score if the arcade managers decided to shut the machine off at night. We were good at pretty much one thing - making objects move around on a screen, and detecting when they collided. Of course, you could in theory do a lot with this. Look at all the classic arcade games from the time period - Frogger, Pacman, Breakout, Pong, Robotron, Missle Command, etc. But at a certain abstract level, your intereaction with these games was fundamentally limited - you could move around on a two-dimensional plane (as in Frogger or Pacman), and potentially cause other objects to move as well (bouncing a ball off of your paddle in Pong). The thing is, despite all the computational power that computers now have we still are really only pretty good at moving objects in 3D space and seeing if they have collided. Quake 4 is basically just Doom, which in itself is basically just good old arcadey Robotron. Computers crunch numbers really well, which means we can simulate physical reality and therefore physical interactions without a hitch. Simulating anything non-physical, however, has proven to be quite a challenge.
There's also a fundamental game design based reason that games are violent. Games by their very nature generally require a winstate. The player wants to get the system into that state, and the other agents in the system (be they controlled by other players or AI) want to prevent that from happening such that they are the winners instead. Only recently have toys and systems without winstates such as Animal Crossing, SecondLife, and The Sims really come into their own. And a common theme amongst them is that they are by their very nature inherently not violent. This is no coincidence. Conflict in systems where physical interaction is far easier to simulate than any other will inevitably lead to violence.
Finally, the third primary reason for the violent nature of games was the emergent demographic these games appealed to. As time went on the inherently competitive nature and physical metaphors of these games caused young men to become the primary patrons of arcades and videogame stores. This is probably the number one reason games today are still as pointlessly violent as they are. Hypercompetitive young men enacting violent power fantasies has fuelled the industry to great heights. And once publishers knew just who they were selling to, it became easier and easier to target this demographic - nowadays, the only two metaphors in existance seem to be either World War II or a generic Tolkien-esque fantasy world.
Of course, this is all a great simplification - there are a good deal of other issues, from developer's creative bankruptcy to a lack of useful/implementable yields from academic research into AI and more. But fundamentally, games are violent because they demand conflict by their nature, computers are good at simulating physical interactions but not much else yet, and the kids who buy these games eat this stuff up.