Well, I can't say games have made me less violent (since I'm usually rather passive, only physically lashing out in blind rage), but they haven't made me any more predisposed to violence either. In fact, I find real life violence appalling; hell, even movie violence is stretching it a bit. I will, however, chuckle in glee while I blow off a random mooks head with a shotgun in a video game. Exactly why it's like this is a mystery to me, but I figure it's fine as long as it stays like that, since I also take great care not to hurt innocent characters. (basically, I play the good guy who only kills bad guys horribly)
My mind occasionally comes up with extremely disturbing thoughts, but so far I have not acted upon any of them, and I doubt video games are to blame for them, because I still have lingering issues from back when I was bullied (one of them being that I tend to bring this up everywhere). I know I just said I'm a passive individual, but there are a few people in this world I wouldn't hesitate to savagely assault if I had to. This is because of burning hatred, not because I'm a gamer.
On a lighter note, I'm probably severely overestimating the threat I could pose to anyone, since my natural elegance is about on par with a drunken ox (minus the strength, given my lanky frame), so I'd probably injure myself before anyone else. Quite spectacularly even, I've lost count over how many times my arms have inadvertently swept something fragile off a nearby surface. That phenomenon can be attributed to vidya games, but I digress.