Reasons n. 3 and 4 are really convincing imo. It's true that a violent videogame may influence a mental unstable person, but then the problem is not the video game per se, but the mental instability.
On the contrary, most gamers who are not mentally unstable are normal, non-violent people who wouldn't harm a fly.
If video games incited to violence then I should have become more violent in those last years since I began playing video games on a more regular basis. You know what, I did not. I'm still the same regarding to physical violence.
Moreover, there's a great difference between "virtual" violence and actual violence, I think. "Virtual" violence is only seen on screen. It only involves the sense of sight, while actually beating someone with your bare hands or with a weapon is very different, because it involves other senses as well. I could spend hours massacring people in a video game, and then, if I ever take a knife and plunge it in another's man throat (and I don't know why I should do it), I'd be scared sh!tless because of the sensations of blood spilling out and the knife tearing through flesh, or, I imagine, the smells. So I don't think video games make us used to violence.