One of the first distinctions to be made when talking about violence is the kind of reaction the violence generates. Some violent acts result in the growth and well-being of the victim of violence, such as a child being punished by a caring parent or in the example of retinas being able to use the bombardment of photons to better understand the world. Therefore, these acts of violence result in a Healthy Reaction.
An Unhealthy Reaction is one in which the victim does not benefit from the violence, and I've noticed two types of unhealthy reaction--overreaction and under-reaction. When a victim of violence under-reacts, the victim misses an opportunity for growth or betterment. Overreaction is the kind of reaction we typically associate with violence--when the violent act causes the victim to visit further violence upon himself or herself. The pain we feel is generated not by the wound itself, but by our brains. It is fully possible to experience severe bodily trauma unaccompanied by pain, though those with leprosy would tell you it's not as pleasant as it may sound at first.
Another important distinction we recognize is between the physical and what you could call mental or emotional, which would be comprised of ideas and emotions, among other things. Both physical violence and emotional violence can lead toward healthy and unhealthy reactions.
The last distinction I want to mention is between apparent violence and hidden violence. My example of the photons hitting our retinas is an example of hidden violence--violence that has apparent consequences, but is not necessarily perceived as violent. By apparent violence I'm sticking closely to the denotation, meaning something closer to obvious, not a chimera or something to not be believed. The violence under question in video games is apparent physical violence resulting in unhealthy overreactions to its victims.
Now that I've established a rough terminology in order to speak more deeply about violence, I hope to now move on to the point I was trying to make from the beginning of this series--that violence is necessary in the creation of art, and that one of the primary goals of any artistic medium is to find the best way to make violence more graphic.