I recently viewed anoter user's blog who asked why we have so much violence in our games, and if it is bad for us. This is a rich and heated topic, so I felt like giving my 2 cents.
I think the reason that we have so much violence in our media is that most of us do not commit acts of violence in real life. Humans have an instincual tendency towards war and violence that emanates from our need to compete in evolution. Because we no longer (at least in developed countries) have to fight for our resources, that desire is not being acted upon. Civilization has caused us to lose our concious desire for violence in the real world, but that inborn desire is still present, therefore, instead of going out and killing lots of people for no good reason, we enter the world of video games to excercise and work out that violence in a simulated environment that does contain a need to fight.
The violence that has existed in our entertainment for centuries has existed because in our endeavour to better civilization, we have eliminated a daily struggle to survive, but our basic instincts, our ids, tell us that we must fight to survive. The video games we play provide an outlet for that instinct.
Let's take Far Cry 3 for example. The game plops you on an island where half of what's alive wants to kill you and/or eat you. This is probably similar to what or cavemen ancestors faced. The games also satisfy our desire for excitement and exploration, by providing us with ample oppourtunities to explore and discover. (you might be able to tell that that is one of my favorite games)
THe question then, is if this simulation is good for us. I personally believe that it is (as long as you are not some sort of mentally unstable person), because I'm a cynic, I believe that underneath all of our civilized behaviors lies savage and dangerous beings. That will never go away. Civilization therefore needs to work to control these tendencies through governance, but also by allowing us to retain a way to satisfy these inborn desires in a way that doesn't hurt anyone, at least, nobody real.