Horse Sh**. You obviously don't know your history. The mississippi had horendous floods before the levee system was put in place, ditto California's river systems that used to flood so bad people could row a boat(cross country)between Sacramento and Stockton in the winter. Marshes and swamps are more important than people? I thought that this was a conservative forum? Where are they?
The places where people mostly live are above the areas they want to divert water in...and if they don't divert the water there, there will be nothing left.
It's impossible to live on a big river without there being floods. The levee system they use now just channels the floods to the spillways instead of onto people's homes, but even then, every now and then a levee will fail...
And one high water year, the old river control where the Missisippi and Atchafayala rivers touch, will give way, and a whole lot more of the Missisippi will go down the Atchafayala. And that will be a real mess.
There are places you need the flooding though. The marshes on the coast need that sediment...They will be pumping raw river water into these areas, rather than tearing down the levees, I suspect...they've done some pilot programs and it really helped the areas they did that to.