I do suspect that video games often have some negative psychological effects, but I don't think violence is one of them. I don't think violent games make you violent, but rather I suspect that all games, violent and otherwise, tend to encourage passivity and isolation.
Why? Games are active participatory interactive devices. Depending on genre, they require the exercise of problem solving abilities, hand to eye coordination, strategic planning, memory, delegation, and I'm sure many other skills. Passive.. No way. Do nothing and you lose.
Watching sports on TV however.. That is super passive. Getting emotionally caught up in an event you have absolutely no ability to control.. How weird is that? Yet if you watch any sport with fans of that sport, they get excited when their team scores, or when someone drives their car around in a circle faster than someone else.
Even social games (e.g. MMO games) result in people sitting alone in a room, not interacting directly with other people. Instead they have control of an avatar which has interactions with other avatars, which I suspect leads to a specific kind of alienation.
Again.. Why? Many MMORPG systems pretty much require you to be part of a group. Sitting in a pub laughing and chatting, or siting in a room alone laughing and chatting over the internet.. The only difference is the physical proximity. And if you can't relate to people except when in close physical proximity, then perhaps you have a problem. How is playing an RPG with a few people you will likely never meet, any different to the typical paintballing weekend corporate "team building" exercise?
I have a few close friends I have never physically met. Some go back over 10 years. Are they to be considered of less value because I can't go to the pub with them? Is a friend crying on my shoulder because she has just broken up with her boyfriend any less of a personal interaction because it happens through email? Should I have felt less worry during the Brisbane floods because the friend who lives there is one I only know because we "met" in an email group?
Someone on the other end of the internet is no less a person than someone who lives a block away.
If these are one's ONLY social interaction. Then yes. There is a problem. Atypical behavior usually is. But the game causing the problem.. Sorry.. I don't buy it. A symptom.. Certainly. If taken to excess, agreed 100%. But nobody is actually arguing otherwise. The guy who spends months playing WOW or something is someone with a real and serious problem. We all freely acknowledge that. We all present this as a cast iron case of someone with a problem.
Also, many games work by encouraging compulsive behavior. Whether you're talking about the stacking of blocks in Tetris or the grinding for stats in a RPG, there are many video game activities that you can't really enjoy without being a little addicted.
Or the building of sets of cards in poker, or the conquest by moving little playing pieces in chess. Or the search for the next piece when making a jigsaw, or the obsessive search for words that fit in a crossword puzzle. Games are repetitive. It is part of their nature.
Can you play a musical instrument? Good enough to let anybody hear you? Did you just pick it up one day and find you could do it? or did it take months or years of practicing the same song over and over to get good?
Do you limit yourself to listening to a song only once?
Ever make filled pasta? Put the filling in, fold over the pasta, seal the pasta, repeat.. Quite therapeutic actually. Once you get a rhythm going, you can just daydream. Your hands go on autopilot after a while.
Knitting? A repetitive sequence of knots made with two sticks.
Gardening? Plant the seeds, weed the beds, water the seeds. repeat. Yet this is a therapy often recommended to people who are suffering from stress.
Repetition is not in it's self a bad thing either.
From personal experience, a quick game of some FPS does wonders for my stress levels. I get to shoot people with no consequences, and they get to get back up unharmed a few seconds later.
If I had no such outlet, what would I do with my anger? Do you think suppression is a healthy way of dealing with it? Because you can't always solve the problem that makes you angry. Screaming at your boss about what a cretin he is tends to get you fired. Shooting some grunt character in a game while PRETENDING he is your boss however, allows you to shoot your boss in effigy with nobody being harmed.
Internalized suppressed anger festers. Externalized anger can be dealt with, and removed. Role playing, writing letters to people, or even aspects of your own personality that you are never going to send. Drawing pictures to caricature aspects of your personality that you would like to be more in control of.. All well established effective psychotherapy devices. See the link yet?
Perhaps the psychology researchers are reacting like the Christian church in some cases. Think they are so against gambling because they see it as wrong? Nope.. They originally disapproved, according to a game history researcher, because at one time, things like casting dice and drawing lots was a decision making tool for them. They saw games of chance as trivializing their tools.