There's actually a version of "Roll the Cotton Down" that seems to lament the end of slavery, and reminisce nostalgically about the good old days "before the war" and then suggests that the black man's lot has only gotten worse since then.
Here are some of the lyrics (just the ones that illustrate my point):
A way down south before the war
We had gay times on the Mississippi shore
When the work was over at the close of day
That's when you'd hear them banjos play
But those good times now has gone away
No more you'll hear them banjos play
The world since then has gotten strange
The black man's lot has sorely changed
Go figure. Maybe it was written by some white slave owner with delusions that slavery had been a good thing.
Your guess is as good as mine.