There is nothing wrong with slavery if one obeys the rules about how to treat slaves. The rules are well defined in Exodus 22. The War on the South was a War against the Torah.
Same goes with serfs--as long as serfs were treated right. But freeing the serfs in Russia did nothing to hep the serfs who suffered the most after that. Not just in the Russian Revolution but even immediately condition deteriorated considerably.
[However I can imagine there were places where serfs were not treated well. But then the remedy would have been to enforce laws about their treatment.]
Serfdom in Europe was due to an arrangement made by people. After the fall of Rome, Europe was in chaos. You had random bands of criminals just basically going around and looting and raping and murdering. To remedy that situation people became serfs around a feudal lord around his castle. In exchange they gave a percentage of their crops to the lord. That is what is nowadays known as taxes.
That is-serfdom was a negotiated deal.
Nowadays white people in the USA are working to support blacks without any kind of reimbursement or exchange. That is the basic definition of slavery. This is the welfare system. Where are the black protet against this kind of slavery?