Economics offers explanations about human behaviour within a very narrow context of "rational" economic activity. To my knowledge, economics has yet to account for the wider range of human experience although many economists try to arrange all behaviours into convenient economic explanations like 19th century physicists explaining electromagnetic propagation through a non-existent ether.

What we are seeing in Christchurch are behaviours we are all predisposed to through millenia of being ingrained into our genes. All our forebears came from groups of people who cooperated and looked after their communities in times of crisis to get through and survive. Those who didn't simply did not leave any descendants because they perished. The selfless acts of heroism and generosity we have seen did not come about because people were thinking about long term costs and externalities, they did so because they are human.

I am sure that rationale economic explanations can be offered for all these behaviours, but this is simply fitting facts to a theory. If the only tool you have is a hammer, then all your problems start looking like a nail. I am sure that Adam Smith would look on in horror if he knew that his modern disciples advocate market forces as a way of regulating human behaviour in general, rather than only one aspect (although an important one) of society.