I've played computer games a lot

And honestly i mostly agree with this research. Gamers are much more friendly than other people(at least vast majority).There was the same research in Russia that proved that competing games(like Counter-Strike/Quake/War\Star Crafts/Crysis) probably make people less aggressive because they express their aggression in shooting people in game but not in real life. Some of my friends are gamers and i can't say that they are violent-on the contrary they are amicable. But every rule have exceptions.
IF we look at people who are almost addicted to MMORPG(Massively multiplayer online role-playing game) like World of Warcraft or Lineage2, we will see that most of them are quite aggressive. This can be explained by the fact that they substitute real life with virtual what makes them indifferent to their actions in reality. Sometimes they transfer aggression from virtual life into real life. I've played MMORPG Lineage2 and i knew some guys who actually had REAL fights because of virtual money/characters. There were even fights between two or more opposing CLANS because of castles ot just to prove that "other clan sucks". There was even a story of a man with nick DVP who played on one of the official La2 servers. His real name was Andrei Ponamorenko.He had a wife and a daughter and owned a computer firm in Ukraine. He had a quarrel with a guy from Moscow whose game nick was CBEPX. Once DVP came to Moscow for a clan meeting and there he met CBEPX(who was a student) and just beat him to death. Probably he didn't want to do that(because he was put in jail for 8 years) but fact remains the same CBEPX died in hospital because his scull was broken. Most of the people who play these games either students(because they usually has nothing to do and MMORPG are highly addict able) and feral and nonsuccessive people(because they don't seek for the success in real life but try to become very "cool" in the game).