Although I know it's not really an answer to the question, and although I know the reason behind the question (Why rebuild in flood/hurricane alley), I can't help but point out that we have rebuilt cities much more devestated than New Orleans.
Hiroshima, Nagasaki, Berlin, and many of the other cities pretty much razed in WWII. (Of course we shared in creating that devestation).
The north west hemisphere is home to all sorts of wonderfull natural occurences (hurricanes, tornadoes, floods, earthquakes, volcanoes, ice storms, sinkholes, etc.) If we didn't re-build after these events we'd have gone back to our places of origin many years ago.
I think the best answer though is one that makes the least sense logically but the most sense emotionally - because we want to. As the Prez said "We can't imagine a United States without a New Orleans". We have the technology, we can make it better, stronger....