It’s not a concept lol it’s a fact of history. Ppl make stories, movies, and books about it all the time. Other than that second couple that unrealistically fell for each other (even then who cares) the rest is not that bad. Black ppl were enslaved, indigenous ppl were enslaved, jews were enslaved; ppl all over the world are enslaved right at this very moment, but it doesn’t mean you can’t write stories about it. If the plot was geared towards making the reader view ‘slavery = good’ then that would be the only reason to cancel it but it wasn’t. It’s the opposite

If this manhwa was released today it would get cancelled so fast what is this plot(I loved it back in the day)