But the racial fears that you refered to led Whites to bar Blacks from the franchise. Once that was done, rich Whites had to give work to poor Whites to keep up their own power in the community, however much they might have esteemed Blacks as workers. White fears of race-mixing and of being outnumbered by Blacks were in evidence even under slavery, well before Reconstruction, so it's not clear how much radical Reconstruction had to do with later race-relations. Radical Reconstruction could be pointed to as a justification, but all the reasons for segregation and the consequent decline of Black craftsmen were already in evidence before.
While I do not want to get bogged down in a discussion of the entire panoply of social factors at play in the South after the War, I will point out something, which you have overlooked in your suggestion that Southern employers would have denied employment to Negroes in order to keep the poor Whites in line. The wealthy class in the South was pushed out of power by the 14th Amendment, which disenfranchised many if not most of them, as a punishment for supporting the war. The Southern patrician only gradually regained political influence.
But as to employment preferences, I again recommend the Frederick L. Hoffman study from 1895. (He was the Chief Actuary for Prudential Insurance, and was writing from a business point of view.)
You might also consider the acknowledgement by Gunnar Myrdal, the Swedish Socialist Economist/Sociologist, who compiled the study that the Warren Court cited in over-turning over a century of legal precedents in ordering school desegregation in 17 States. While it is not a part that the "Liberals" or judicial activists like to cite, Myrdal acknowledges in his book that his ideas could ruin the Negro middle-class in the South. (Of course, as a Socialist, he had no great concern for the middle class, who are after all the principal target of most Socialist movements.)
I will grant you that the issues are quite complex, and wish that I had more time at the moment to more fully develop them.
William Flax