That is really disturbing. The violation of the 4th and second amendments is very disturbing to watch. Frankly I do not understand the mandatory evacuation at this point. They are in the process of draining the city. People should be returning to their homes, not being forced out.
Add into the mix the fact that there is no infrastructure whatsoever, it simply is not realistic to expect to survive in New Orleans until the cleanup is done.
With those two factors - and the fact that it is an emergency zone under all but martial law - it's not hard to see why the Fourth and 2nd Amendments do not apply. The Fourth Amendment prohibits unreasonable search and seizure; it's eminently reasonable to expel people from a public health danger.
Fear. Fear of getting dirty. Fear of liability of asking others to get dirty...etc.
A local story ran of an old mercury thermometer breaking within the city limits and having to call out the HAZMAT team.