@Misticsan You are over-reacting. The world is currently falling apart, I would not be surprised if slaves become a thing (in the "west) again in our time.
Mind you, slaves are still being sold in the middle east and parts of Asia, and supposedly in parts of south America.
I also feel that many people forget our own actual history. Slaves did have some sense of rights in the past. Maybe not America in particular, but it was indeed a thing.
I think the thing that causes the most interest/controversy in these "isekai" stories is a legal slave trade.
If there was another world war, or some sort of major civil war, people would not be put off of the idea of a slave trade.
The only thing holding society together as it is, is a sense of comfort. As soon as that comfort disappears, I would not be surprised if "medieval" customs made a "sudden" comeback.