slhno at Stop The Flooding lists the reasons why Americans should care about adequate levee protection for New Orleans.
As to New Orleans, the flawed levees that the Corps built did not withstand what they were designed for. These levees were built with federal funds by the federal government. Homes were fine after the passage of Katrina; it wasn't until the levees broke when the flooding occurred. The levees were not topped. Rather, they fell over due to defective design.
Read the whole thing.
Remember folks, your taxes paid for this.