I understand this.
I just find it ironic that we are ALL expected to act like ... well ... to act "civilized."
We have social and cultural norms...
But when [exceptions?] occur, like Klebold & Harris, people scratch their heads and wonder what went wrong.
If I was an evolutionist, I would say, "Nothing went wrong. Two guys just went rogue ... like an elephant ... and did things reminiscent of our ancestors."
Clearly something went very wrong from the point of view of a serious breach of socio-cultural norms, and even in terms of expected 'natural' behaviour; but developments in the brain sciences suggest that behaviour of this kind is a consequence of the influence of particular life experiences on particular genetics.
For example, it's estimated that psychopaths make up around 1% of the population, but folk-psychopathic behaviour is much less common than this; studies have found that an unstable and/or abusive childhood is common to those who behave badly, and a relatively stable and happy childhood is common to those who behave well - and in the conforming individuals, their lack of empathy gives them a distinct advantage in certain careers.
As Sam Harris has pointed out, the more we know about the detailed history of antisocial individuals, the more we discover the impacts of events outside their direct control - as the case of
Charles Whitman (the Texas Tower Sniper) shows, physical changes in the brain can have drastic effects on behaviour. So it's clear how much influence changes to the function of body and brain can have on individuals - even in the face of psychological interventions and their rational desires to do otherwise; more common examples are addicts, OCD, the obese, anorexics, phobics, dismorphics, etc.
We also know that life experiences change the way the brain develops and is wired-up; for example, the
London cabbies whose brains change as they learn 'The Knowledge'.
So, yeah - something went very wrong when two guys went rogue, but that doesn't mean we just throw up our hands and say, "they were just born evil", or "the devil took them"; it's likely that their incipient problems could have been spotted earlier, and probable that if their life experiences had been more positive overall, they would not have gone rogue.
These developments have interesting implications for the concepts of free will and moral responsibility - it's another situation where the closer you look, the less distinct where to draw the line becomes, or even whether to draw a line at all.