Is a problematic manga for the one of the main themes in it and will probably never get out of Japan, and we are fine with that, don't like it go away, anyway the slavery in it is literally world's away what is still present in ours.
Comic characters have no right people.
And in isekai our laws don't count, and even if they do, it would be the laws of what country? North Korea sells their people as slaves but how much do we hear abut that?