I've always though that if there was some clear, unmistakeable link between games and violent behavior; there would have been mutliple discoveries in psychhology a long time ago with the amount of research that has been put into this.
In the 80's, there was the same discussion and subesquent research done on movies, in the heyday of Arnold, Stallone, Van Damme and other action heroes, it was argued that these movies caused people to be violent.
I guess one could say that it is different participating in the violence through an interactive medium but movies are a lot more realistic in their portrayal of violence for obvious reasons.
The research on violent movies hasn't really yielded anything that shows a correlation between watching them and becoming violent, or even increasing the violent nature of individuals who are already prone to such.
I suspect; after 30-35 years of the same research on gaming, the results will be much the same, the primary reasons this is such a debated subject is, in my opinion;

A: The average person is rather ignorant when it comes to gaming, its culture and suncultures and the motivations behind playing video games.

B: It is the perfect scapegoat; a private industry that can alleviate the responsibility from parents, governments and institutions such as schools for kids behaving violently.

games or not or what ever the media is, people easy to influenced by their surrounding like friends, neighborhood and mostly family. So Video games is one of them, even if a person playing non violent games in violent society or family, the person will still influenced by the closest factor which is family.

Thanks for all the great replies guys!

Do you mind giving some examples? Not disagreeing but I would like to gather as much info as possible.

Family is the first unit of socialization, definitely; but the media definitely has a large hand as well. According to Albert Bandura's social learning theory, people learn through observing, imitating, and modeling. He conducted his famous bobo doll experiment (which measured a child's behavior after watching an adult act aggressively towards a bobo doll and either get rewarded/punished/no consequence. In this instance, they were likely to exhibit aggressive behavior like the adult had. One could argue that, according to the social learning theory, children might imitate what they see in a violent video game.

Of course Bandura's experiment still had plenty of criticism, as well.

http://en.wikipedia.org/wiki/Bobo_doll_experiment#Results

Welllll a lot of studies have had similar results. One could argue that the result of their findings is the ERSB rating on games and movies. To your other points: I think the reason this is still such a debated subject is because nobody can seem to agree on it. After Columbine, research increased, but early research was shitty. A lot of the more modern research has resulted in better findings.

This is a good counterpoint by Dr. Christopher Ferguson responding to a piece by one of the main names that you may see trying to link video games to violence:

http://www.cnn.com/2013/09/20/opinion/ferguson-video-games

Also, I think a lot of the things that I am saying are fairly self evident.

Lets talk about "aggression" for a bit. Whenever I hear a study say this word, I almost instantly write it off. Why? Well, first of all, the definition of aggression is fairly vague, and it can't really be strictly defined. Second of all, a lot of different things cause aggresion, from sports to physical activity and I believe that the competition is the primary factor in increasing arousal (an interesting piece about how losing causes "aggression" and not violence: http://www.forbes.com/sites/insertcoin/2014/04/08/at-long-last-video-game-aggression-linked-to-losing-not-violence/ ). Third, there is a monumental difference between someone getting excited/aggressive and someone being in a position where they would commit a real world act of violence.

Fouth, lets look at some of the ways of measuring aggression:

1. From your first article posted in the OP, the measure of violence is something called the State Hostility Scale. This is a survey which uses a one to five scale for statements such as "I feel friendly" and "I feel amiable" and "I feel offended". Seems like pretty weak ground to stand on if you are trying to assert that someone saying "I feel like swearing" is in any way a reasonable way of linking this to real life violence.

2. The third article in the OP uses a similar survey, except this time using statements such as "If someone hits me, I hit back". Once again, a huge separation between any real world actions and answers to survey questions.

3. This article ( http://public.psych.iastate.edu/caa/abstracts/2000-2004/02BApspb.pdf ) uses "story stems" to show that people who play violent video games have increased aggression, meaning that they have the players complete a story.

4. Other studies use things such as facial recognition software (or something similar) to detect subtable changes in the emotion of the players faces.

My point with all of this, is that these are laboratory studies which take some shallow definition of aggression and try to stretch it to imply that this in any way indicates that video games are causally linked to real world violence.

I definitely agree that a lot of the research is vague and/or bad and/or slightly biased. I have a theory that research spiked after Columbine, and since then everyone has been trying to clamp down on a lot of entertainment aspects so as to avoid anymore shootings, all the while only seeing the forest for the trees.  I ended up reading a lot of studies because I wrote a paper on the topic, but none of the studies seem to be able to relate laboratory induced situations to real life results.

I do however think that ERSB ratings need to exist, and that parents need to follow them.

If a parent buys a kid a mature game and the kid does something stupid because of that game it is the parent's fault. That's just my opinion, though

That's more than opinion. It's a fact that it would be the parents fault. But you bring up a good point; ratings exist for a reason.