Well, if you think about it, it was bound to happen.
The only people who didn't flee the city besides the elderly was the poor and undereducated population of New Orleans.
Now take those same people, put them in a sweltering hot dome without food, water, medicine, or adequate plumbing.
That just pissed them off, which led to the looting and violence. When Wal-Mart opened their doors and said "take what you need" - they went on a shopping spree.
They just didn't know any better.
edit: Not that I condone anything that's going on - the whole situation is retarded. But at this point they're all starving and it's a fight for survival.