Banning them sounds pretty extreme to me- I know little about waste water management but surely the systems can cope with some carrot scrapings and a bit of mashed potato off the side of the plate! Can it be that different from whatever comes down the storm drains- leaves, etc, or whatever comes down the sewer, in terms of treatment?
At least in the wastewater plant it can be recycled and used for making fertiliser. Also, there are no transport costs invovled because it travels by pipe. I would have thought that it was (potentially at least) pretty environmentally friendly.