Huh... you know, with all of these isekai slave style stories, the MC's slave always ends up a debtor slave. The only time a criminal slave comes into play is with a scumbag antagonist (or maybe an MC will find one where the crime was a setup, or it was political [and she's secretly a princess]). And the MC's slaves never end up from 'human' trafficking, it was always too many mouths to feed or parents' business going under, etc.
Also magically enforced enslavement, rather than just law based, which can be arguably way worse (stopping the slave from running or betraying without it killing the slave, or [more rarely] it comes with brainwashing enforcement so the master can order you to believe what he/she wants). At least with criminal slaves, you can argue comparably about that treatment vs imprisonment and prisoner labor and whatnot. For debtor slaves, its into being evil that they can be forced into life-or-death combat, or used as sex slaves, etc. If the land being portrayed wants to pretend its righteous-ish about its slavery, there should be enforced better treatment. Even criminal slaves should have some levels, not every crime should be a death row / sex slave sentence.
I guess, if i have to see slavery in these types of stories, i'd like to at least once see an MC in a slave isekai story actually have to deal with someone who doesn't want to be his slave. Maybe free her (cause it'll always be a female slave for a male MC), she leaves, maybe then have stuff happen and she ends up as an MC employee under contract. Instead of always being a slave who tells the MC not to free her cause her enslavement to him is 'precious' to her, or something.
Not that I can't deal with it being the same 'ole trope. I do read Slave Harem.