You uh... don't know too many people from New Orleans do you? Ask them to move and they will look at you as if you'd grown another head. Maybe moving elsewhere is easy for you, upper-middle-class person with marketable skills and no loyalties. But to them it's like saying "Hey, why don't you just walk away from everyone and everything, the people and sights and smells and sounds, you cherish? You won't? What are you, insane?"
It's more than just irrationality. I've never been there, but from what I've seen New Orleans has a unique culture that you can't find anywhere else. It's not irrational to want to be part of that culture, even if there's the occasional risk of flooding.
