I don't think that computer games do make young people violent (although lag might). I think that it is down to the individual and the parents. If the person is easily influenced and is likely to do mimic something they've done on a game then the parents simply shouldn't be letting them play the game.
The computer games do make young people violent. It is a known fact that the young are easily influenced by things that are appeal to them. The computer games company make their products colorful, vivid and exciting to attract young people to spend money on them. However, the prevalent violence in modern computer games such as the popular game StarCraft, teaches them to exert power on others, to destroy the weakness and find success in war. Young people, especially the males, like to find their masculinity in such activities, identifying the success in the digital world as success in the real life. Therefore, they are subconsciously affected by the ideas in virtual world by believing in power and cunning rather than friendship and love.
The world is not perfect and what shouldn't be done may still be done in reality. We cannot count on parents to help their easily influenced children refrain from playing computer games. It is possible that the parents are too busy to spend enough time in maintaining discipline, and thus let children play the game unnoticed.