You, like most people, are overlooking a few facts here. New Orleans used to be well inland and above sea level. A long series of environmentally disastrous policies lowered the water table, removed natural barriers, concentrated storm surges, and generally guaranteed that NO was a disaster waiting to happen.
Unfortunately the government and Army Corps aren't legally liable for severe technical malpractice and rank stupidity. This suit slips through a loophole in the legal immunity the government gave the Corps.
New Orleans could be saved. And the cost of abandoning a major city is immense, far more than building better hurricane defenses. Building better hurricane walls will cost far more than restoring wetlands, allowing the water table to recover, and re-engineering the waterways. Of course, the best/cheapest solution is probably the one least likely to be selected by our broken political process.
And the cheapest solution of all (short-term) is to blame the victim and do nothing. It's worked really well so far.
The optimum committee has no members. -- Norman Augustine