Actually it's the Sierra Club's fault
Levees in New Orleans would have survived if not for a 1977 environmental lawsuit filed by the Sierra Club.
(from The Federalist Patriot)
A congressional task force reported that the levees that failed in New Orleans would have been raised higher and strengthened by the Army Corps of Engineers were it not for a lawsuit filed by environmentalists led by the Sierra Club. A 1977 lawsuit filed by Save the Wetlands stopped a congressionally funded plan to protect New Orleans with a "massive hurricane barrier." U.S. District Judge Charles Schwartz, Jr. found that New Orleans' hurricane barrier would have to wait until the Army Corps of Engineers filed a better environmental-impact statement, as the region's natural environment "would be irreparably harmed" if the project continued as planned.
Subsequently, the Corps opted for a plan to strengthen the city's existing leveesat twice the cost of the original planto withstand a Category Three hurricane. With the exception of the environmentalists who now blame George Bush-spawned global warming for the hurricane, we all know how the story ends.