This article again raises the age old question of nature vs nurture once again to explain why people tend to be violent or exhibit violent behaviors. Nature vs nurture basically asks the question whether our upbringing and surroundings (nurture, raised), or our inbuilt and genetic make ups are the key to explaining our behaviors (nature, born). There are certainly factors of both that can be argued for in determining where any human behavior comes from, and neither can ever realistically be completely proved one way or another.
On the Born side of the argument there is clearly a case for individuals who for no apparent reason become violent and even some serial killers, who have had no life experiences that would warrant them becoming violent as a response. People with perfectly normal backgrounds and upbringings sometimes become extremely violent with no environmental factor being the catalyst for these behaviors to develop.
Certainly for some individuals there are chemical imbalances that they are born with or are predisposed to develop at some point in their growth and development that mean that they are far more susceptible to becoming violent and to developing disorders such as schizophrenia, which their upbringing can have no effect one, negative or otherwise.
On the other hand for the raised side of the argument, there are hundreds of cases documented where victims of abuse become abusers themselves, and if not then certainly become more violent in general as people. There are several famous serial killer cases where they certainly appear to have been created as the monsters they become over a number of years a result of decades of abuse and violence directed towards themselves before they begin to prey on others.
People who are exposed to violence every day of their developing lives are certainly a lot more likely to become violent themselves, as well as having deep seated self esteem and trust issues as well. Over the years of abuse they begin to see this behaviors as normal and tend to fall into a pattern of the same behaviors themselves, which often leads to self loathing as well, because of course they have their abusers and yet cant seem to stop themselves becoming the same.
Overall i don't think this debate will ever truly be resolved one way or another. There is supporting evidence for either case, meaning to me that both are true, and that both can be reasons, rather then just one of them being the case. Many people might argue one way or the other, but the true answer is that either or both arguments can be true depending on the particular case in question.
A certain famous quote from a study into alcoholism by an unknown psychologist comes into mind in helping to explain this debate. the study found that a particular alcoholic was found to have two sons, one of which was an alcoholic and the other was teetotal. When asked about their drinking habits they both answered the same. With a father like that, what do you expect?.
I think this somewhat explains this debate as well, that although upbringing can be a factor it can also produce the opposite result and that although nature is a factor as well it isn't always triggered and can sometimes be treated before the onset of violent behavior.