According to Washington, what were the economic , political , and moral repercussions for the white community when they abused African Americans ?

I'm not sure where in the book you are referring to but I think he means that the white community becomes desensitized to their own violence and hate. Also the implications of an economy tied with slavery could not last. As society moved on and slavery eventually is abolished the cotton farms and relative economy of the South becomes starved of free labor. Politically, we see how the Civil War played out for the South.