What kinds of things which are currently considered signs of social progress are also things that an average educated person from the U.S. of the 1800s would find horrifying?

And of those, which of them should we still find horrifying today?

In this example, though, we're the Confederate War Veterans - it seems rational, given our preferences, to crush the dreams of the future. (Or to alternate to an example with different affect: it's rational for, say, an idealistic young lawyer to take precautions to ensure she doesn't become an old scumbag lawyer, even if she know the old scumbag would be very happy those precautions had not been taken.)

Of course, perhaps Jim Crow was not the true implementation of Confederate CEV; they would have preferred different things if they had been more informed about the world and more the people they wanted to be, and so on. But in that case Confederates should expect that their future selves should more faithfully execute the real CEV as they become more informed, unless they don't trust themselves (suppose I like fairness but like myself being on top slightly more, and that at after a certain point future-me is sufficiently unlike me that I'd prefer he not be on top (even though he will, since he will my preference set) - in that case it's rational for me to precommit to stepping down after a certain time.)

So upon reflection this is a valid concern to the extent that 1) we don't trust ourselves to implement our current CEV better than our successors and 2) we don't trust our precommitment mechanism to work either. Of course "our" CEVs probably vary enough that there's not a single useful answer here.

You probably should read a little more history. Things were better for most blacks in 1910 than they were in 1940. Woodrow Wilson's election, and his subsequent expulsion of blacks from the civil service, started a period of decline for blacks that was deepened by the Depression, but had strongly started improving after WW II. Brown vs Board of Education was a result of the change not a cause, and "Civil War" veterans were irrelevant.

Thomas Sowell has written on race problems, notably in Economics and Politics of Race and large parts of his memoir, A Personal Odyssey. His discussion of Brown in the latter is particularly interesting, he was attending Howard University at the time, though a lot of comments about it and its effects are spread throughout the book.