I think you've discovered the two realms of personal viewing we should be aware of — sex and violence. These two realms relate to the commandments regarding human life: — sex, its beginning and — violence, its end. Since human life is sacred, as being the image of God, we need to respect this sacredness.
Watching sexual images inappropriately excites the lower nature. Watching violence, for most people, doesn't have the same effect as with sex; however like sex it can slowly desensitize us to the horror of sin, and lead us to wanting more.
When I was a kid we used to play cowboys and indians, or cops and robbers, and we would "shoot" each other with toy guns. I don't think this made me more prone to violence, or even desensitized me, however, video games and contemporary movies tend to be very graphic and gratuitous. And often today, unlike when I was a kid, the violence is directed at the good guys or the innocent, rather than the criminals.
So, I don't think there's a hard and fast law regarding the viewing of violence; but if you believe something will lead you further away from God in heart or in mind always try to avoid it.
We live in a culture filled with illicit sex and violence, so use your gift of prudence and do your best.