I think that anyone can be trained, or brainwashed, if they absorb too much of a certain media -although this is yet to be proved-, and it is true that most games are designed to be emotionally and psychologically riveting - lest people get boarded or uninterested. However, if you balance your gaming with a, quote-unquote, "normal life" you should be fine, barring some other issue, and should not worry about the negative consequences of your media - if any exist. Basically, unless you are playing Halo 3, Half Life 2, or any other game for prolonged periods with no outside interaction -by long I mean many months, if not years- you should be fine - although I will admit that games like Call of Duty are more likely to be harmful then, say, Peggle....