Video games don't cause violent attitudes, they cause aggressiveness. Aggression can take many forms besides violence. It can fuel competition, which helps in school. It can cause motivation, which helps in the workplace. Its just a matter of one group only seeing the negative aspect.

Same think happened in my English class a couple of semesters ago. Teacher had us read material about television and video games causing aggressiveness. Then he had us read material about negative effects of violence. Then he had us right a paper on how it was necessary to get rid of television and video games. I dropped the class in the end.