I would think it is reasonable to assume that when a major city is supposed to be completely evacuated, some military contingent needs to be mobilized at the same time to prevent looting.
Yep. Hindsight is 20-20. But obviously if you need to evacuate and entire city. While the people are leaving the Military needs to be arriving.
This is absolute chaos and is quickly becoming inexcusable IMO.
True. But the issue is scope. Isolated looting is one thing, and that's probably what they were expecting. This sounds like (though it may not really be) something a lot bigger than "normal" looting.
At any rate, I think a bunch of disaster plans are going to be changed to account for the magnitude of looting in NO and other affected areas.