My opinion on this matter is rather hazy so bare with me and try and make something of it.
Firstly, in some ways I AGREE that violence in videogames CAN make people violent. Perhaps not physically or by buying a gun and shooting someone, but verbally. I have always believed that people saying someone killing another person due to playing video games is dumb. Me killing AI computer people in a game does not make me want to do it in real life, but I have been very verbal to my parents when I was younger playing violent and FRUSTRATING games like Call of Duty.
I used to shout, throw my controller, be short tempered and become very blunt and verbally aggressive when I used to play Call of Duty. Not so much CoD1,2,3,4 or W@W, but deffinitly on MW2 and BO. These games made me compete, and as I believe myself to be a very good player, getting killed in some un-fair or unbalanced way whilst trying to use weaker weapons or something new made me become extremely FRUSTRATED. It wasn't the violence in the game, it was the FRUSTRATION and ANGER that came with playing the game ONLINE.
I have since stopped playing Call of Duty. I reached 10th prestige on all but 2 (W@W and BO) and when I hit 7th on BO after playing 4 months, I realised, I can't do with this stress anymore. I quit about 4 months ago and haven't had a single argument with my mum, dad or girlfriend and I have since played exculsively Single player and co-operative with minute amounts of online MP with friends FOR FUN and I have become a new person. I now watch movies, play lots of different games, read, draw and am currently teaching myself everything I need to become part of the Games Industry and I can happily say I am on my way.
So in answer to the topic, no, I don't believe Violent Games make people Violent.
I DO however KNOW that extremely competetive ONLINE games are FRUSTRATING, STRESSFUL and make people ANGRY when they are playing, whether they are casual or hardcore and I am becoming more and more against LEADERBOARDS and STATS and I feel that KILLS AND DEATHS SHOULD BE HIDDEN in games so that people can ENJOY them and not become FRUSTRATED.
Thanks for reading my input, sorry for the wall.