We don't know much about what motivated the shooting massacre in Newtown, Connecticut.
The peculiar irony is that I just ran across Peter Singer's review of Steven Pinker's book, The Better Angels of Our Nature: Why Violence Has Declined. The evidence seems convincing that as a whole, people today are less likely to die at the hand of another compared to earlier points in human history. Yet some pockets of higher violence remain, such as in southern United States.
Singer writes: "Pinker argues that at least part of the reason for the regional differences in American homicide rates is that people in the South are less likely to accept the state's monopoly on force. Instead, a tradition of self-help justice and a 'culture of honor' sanctions retaliation when one is insulted or mistreated. Statistics bear this out — the higher homicide rate in the South is due to quarrels that turn lethal, not to more killings during armed robberies — and experiments show that even today Southerners respond more strongly to insults than Northerners."
Was honor—or the lack of honor—a cause of this son's matricidal rampage in Connecticut?
That's perhaps too simplistic. Yet it is important to recognize that the feeling of honor (or being properly respected) is a powerful instinct; when others fail to reciprocate our emotions the result can be rage:
"But if you have either no fellow-feeling for the misfortunes I have met with, or none that bears any proportion to the grief which distracts me; or if you have either no indignation at the injuries I have suffered, or none that bears any proportion to the resentment which transports me, we can no longer converse upon these subjects. We become intolerable to one another. I can neither support your company, nor you mine. You are confounded at my violence and passion, and I am enraged at your cold insensibility and want of feeling." (Adam Smith, The Theory of Moral Sentiments, Liberty Fund, p. 21)