Unfortunately, we see violence and aggression almost everyday, either in real time, or on the TV news. Some of the aggression seems almost an act of simple stupidity as opposed to a well thought out activity. For example, road rage is a good example of spontaneous aggression brought about either by frustration, or brain chemistry gone wrong. As most drivers know, it is a frequent fact that we see other drivers that do some unusual things while driving. They may fail to signal lane changes, cut in front of others, or just change lanes without  considering the other cars on the road. And, in complete disclosure, I have been guilty of making poor choices, particularly at merge locations, where I inadvertently offended another driver.  But, if it happens to me, I don't automatically go for a gun in the glove compartment or try to run the other driver into a ditch. We make decisions based on several basic pieces of information. Did the other driver intentionally mean us harm? Or, did the circumstance happen by a simple mistake. I believe that most of us will try to distance ourselves from the offender if it appears to have been intentional. If it is a mistake, we just move on after a few quiet expletives. But others will try to destroy the offender. And as Shakespeare noted "therein lies the rub"!
The question is why and how the decision is made to avenge the audacity of the other stupid driver. Almost one year ago on this page I posted the subject "Evolution" asking if we are as highly evolved as we are led to believe that we are. My general thesis in that post was that we are not highly evolved and still operate with the basic tools of the early cave dwellers. We are, as societies have changed, controlled by social convention, but it seems to require only a small incident to get us to revert to a very basic instinctual reaction. It is only a blink of the eye in cosmic time that we have been "civilized" with rules, laws, and mores. So. I continue to come down on the side of nature with regard to aggression and violence.
But, there are divergent views and the question will probably not be answered in our lifetimes. I did some hunting around for a balanced look at the issue and found a 2002 article on Serendip.com written by Sarah McCawley at Bryn Mawr College here. Some of the footnote references have not been updated but it is a good start in understanding both side of the issue. I am always open to a change in thinking, and  welcome comments. But right now my serotonin level is up so I will stay off of the roads today...