I just listened to 3 solid hours of talks on freshwater diversions and it was very civil even though there was disagreement on a few things, mainly the cause of the land loss below Caernarvon. There were 2 oceanographers, 2 geologists, and a plant ecologist. Some pointed towards Hurrican Rita, some towards the diversion for the land loss. One of the take home points was that for every acre of dredged canal you lose 4-5 acres of marsh. One of the things that they all agreed upon was that saltwater is the worst thing that can happen to a marsh. There are different types of marshes, and they can all tolerate salinity differently but saltwater for long periods of time will kill it all. The poster child for this is Sabine NWR where Rita brought saltwater and kept it on the landscape for long periods of time. You can see it on Google Earth and any aerial photos that the land was lost and isn't coming back. THIS is what you get when you have saltwater come into a system for long periods of time.
The people that are 'benefitting' from keeping saltwater out of that marsh is everyone in Louisiana
Ask Vermilion Parish rice farmers about saltwater intrusion and what it does to crops (i.e. their livelihood)
widgeongrass can handle a little salinity also