Yes, violent video games can provoke aggression in some, but for others, like me, it is a medication for aggression. I have psychologists orders NOT to quit playing violent video games because of my history of anger issues, and this is coming from an ARMY psychologist. Getting pissed off and want to kill someone? Jump in a game and do it! There are a lot of people out there like me who self-medicate on violent video games, it is a much healthier way for one to deal with anger compared to the alternative (getting a gun and going "postal").
in my case it's not the violent games, but frustrating ones.
well, some are violent and frustrating - ever played ninja gaiden on ps3 ? :> ( god of war 2 is also very frustrating ). or gradius / ddr games at higher levels / gran turismo licence tests / wipeout hd racing at elite difficulty. or the games where even "normal" difficulty is way off the scale that are the most infuriating.
games with pointless violence are a different thing, though.
fortunately i always stop playing before getting really angry due to my continous failures. even when i am angry i never take it on anyone/anything. that's also a reason i prefer not to play online - i worry that i might actually get angry at somebody who beat me (because it would be obvious) or get seriously addicted.
i give such games a try once in a while to see how long i can keep my calm. and i'm slowly getting better at this, and it's a great anger management/patience exercise (if you can keep things under control). it's all a matter of knowing your limits, and knowing when to stop, which is something many people don't do. and a matter of not taking a game too seriously, which is something even more people cannot do.