Before and besides stating that the “videogames encourage violence”, one can ask: “why do people prefer violence in videogames?”. A gamer could say: “Because the violence in games is not real violence, it is just the reflection of the competition in the essence of the game.”
As a matter of fact, game theory tells us that there are different kinds of games, and small differences in game rules may encourage players to compete or cooperate, or even both by different aspects. For example, Counter-Strike, one of most debated games, includes intra-team cooperation and inter-team competition. Latter war games like Call of Duty 4 improved on the intra-team cooperation, thereby escalating the competition between teams.
One can still insist on asking “why war instead of any other human activity?”: Why don’t eliminated avatars and enemies walk outside a chalk-drawn border and wait until the game ends, but they drop dead with blood everywhere? It’s simple: Because avatars and game characters don’t have a privilege to exit the game and continue existing. Eventually, like other digital data, they have to be destroyed, deleted from the memory when they are done. They’ll either dissolve into thin air, or they shall return back to the game every time they die, like in MMORPG’s.