There is a very compelling movie about Shelby Lee Adams that is a must see for photographers or anyone interested in his work.
Apart from the strange beauty of his portraits, I think the best thing about the work is that it explodes the minds of the politically correct arts intelligentsia. They simply cannot get past the idea that this man has spent decades photographing such people, whom the PC crowd simultaneously a) claims to want to protect due to their low social status; and, b) loathes due to their low social status, perceived lack of intelligence and urban refinement.
The "exploitation" accusation is the classic Argument from Intimidation. It is not designed to encourage free thought and discussion, but rather, to shut it down.