I'm not persuaded by the rational calculation -- poorer people, because they have less money and thus stock less food, are more likely to resort to desperate measures. Human beings are not robots, and they don't behave like Vulcans. I doubt people's personality will just suddenly change in a disaster situation; e.g., a law-abiding citizen would just start raping and pillaging all of a sudden. Besides, if you accept the rational calculation above, you then must accept also the following:

1. "More likely" [to resort to desperate measures] just means "sooner." So that means there is no difference between the poor and the non-poor. They are all automata that run the following program: HUNGRY? SMASH THINGS!

2. What's to stop one of the non-poor from making the following, totally logical calculation? "The poor people, because they stock less food, will resort to desperate measures sooner. So I need to loot the stores before they do."