This thread is interesting as I am currently reading and listening a bit to William Marvel's work. Now Marvel is not a neo-confederate. He openly argues the war was over slavery. But his civil libertarianism (I assume that is the ideology that motivates him, but he is not as crude as Misean critics of the Union. Also the guy does know how to write and speak, and does do some impressive original source research ) leads him to be severely cynical with the USA war effort and accept secession as a right and legal under the US Constitution. One of his more problematic for me arguments in Mr. Lincoln Goes to War is that while one cannot argue that every alternative history if no civil war happened would be better than what took place, he does not believe it would be worse. I question that, and I am glad for thread like this that help formulate some thoughts on it (though in this case the war still took place and south just won. He argues for no war, Lincoln just accepting the loss of the seven deep south states). I think the most important point is giving indicators that the USA itself would be a worse place in this scenario (more institutionally racist).
It also is funny when I read supporters of gradual compensated emancipation arguing that it would had been better for US race relations (Marvel posit it as hypothesis though he is not willing to say if he believes it would be. To his defense he does openly argue that any thoughts on the morality of the civil war do rest of solving the insoluble equation in his mind of weighting the lives of the 620000 that died in the war vs. the millions that would stay in bondage for three-four generations if it did not happen), when the example of Brazil pretty much shows that no, you would more or less get the same bad result with the de jure emancipation we got from the war.
So I think the bad here are realistic. Open Legal Chattel Slavery could and did survive into the 20th century (Mauritania), Leopold of Belgium was permitted to run what was a massive plantation into the 20th century, and slave labor work fine for the crude industrialization practiced by the USSR and others.
The good news is that I expect the good to also be realistic. That might mean lots of tragedy, lots of slow reform, lot of violent revolt, but ultimately some catharsis.