It is a lie. New Orleans isn't "the hold of a slave ship". It is the milk farmers fields and barns, where his cows live.
The problem is that the farmer left when the storm came and left his cows to weather the storm on their own.
Build their gallows high
And that is a lie.
Well yes, there is an analogy there. It was other blacks that sold the blacks into slavery, so you can appoint Mayor Nagin captain of the ship and Jesse Jackson is the auctioneer...