Currently, there's a common argument that whether or not playing violent video games (or watching violent imagery on TV or movies) causes aggressive behavior in children. The video of this week's discussion showed that, when children watched the video "powerful rangers", they became aggressive and fought with each other but when they watched the video Barney dinosaur, they became happy and danced together.
It seems that violent TV shows are positively correlated with violent behavior. However, in my opinion, they just imitate the performance of the TV show but not actually have violent tendency. In my view, playing violent video game maybe cause the aggressive behavior to some degree, but the genes of the kids and the environment they grew up play a more vital part in aggressive behavior.
Why some people prefer to play violent games? I have two main reasons.
The first one is due to the environment they grew up. If the parents always punish their kids like punch or hit them at home and the classmates of the kids always tease them in the school, they will feel depressed and angry and need some way to let off steam. This kind of people will choose to play violent video games. Since they are not given enough love and care from their parents and peers, they become aggressive.
The other one is because some kids born to be aggressive and they just have aggressive genes. They choose to play violent games because they have aggressive personalities and they love those violent things.
Overall, I think in many cases aggressive people choose to play violent games so there's a positive correlation between violent games and violent behaviors. But we still have to design experiments to explore if playing the video games will improve the level of aggression of people.