That's generally not true.  There are a number of studies that show a correlation espeically when focusing on M rated games, 18+ games, shooters in general or games with specific violent factors. 

Of course all that correlation shows is that violent angry people like to play violent angry videogames.  It should be no surprise that people who like to go out and punch people like games in which they punch people, and TV shows in which people punch people, and books about punching people.

There's a saying that goes "Never let a good tragedy go to waste".

People want simple answers to complex and deeply rooted issues. Its easier to scapegoat a specific firearm or video game than it is to discuss and debate why people do violence against others. The answers to those questions aren't as convenient as people want them to be. So they go after the easy (and very wrong) things.

In which case, Halo ought to attract the sorts of people who like to beat up aliens.

So, people who would be members of Cerberus if they were born 200 years later?

Your second paragraph is true, but the reverse of it is not. I love violent angry videogames, and I don't consider myself violent or angry, and some of the most violent and angry people I know are those who don't game or only do so casually (FIFA and such).

If you disagree, you should take it up with the ESRB. They're the ones who give all the games M ratings for "blood, language, violence," and let's not forget the "online features that may expose players to unrated user-generated content." The M-rating meaning "don't sell this game to customers under 17."

I totally agree with you on this.

It's the parents fault if they bought their 8 year old son CoD or Halo. You can't blame it on the games when they're the ones buying them for their son/daughter to play.

http://www.esrb.org/ratings/synopsis.jsp?Certificate=32424&Title=Halo%204  [minor spoilers]

Without the spoilerish bit:

This is a first-person shooter in which players control futuristic super-soldiers who engage in military campaigns against alien forces. Players use pistols, scoped rifles, machine guns, grenade launchers, and futuristic weaponry to kill enemies in ranged combat; battles are highlighted by cries of pain, realistic gunfire, and large explosions. Stealth moves (i.e., “assassinations”) can also be used to attack enemies from behind (e.g., snapping their necks or stabbing/impaling them with bladed weapons).

That does sound a little excessive for a nine year old, but a 13-14 year old? Would you really need to be 17 to be emotionally capable of handling what the ESRB describes in that synopsis?

Well yeah, it's not like correlations are 100% things.

I'm just saying, there is science there, generally the main issue is that most people don't understand how scientific research and thinking works, so they try and ban things