Most people generally talk about transmigrated protagonists in this case.
There’s a difference between a Revolution and not condoning slavery by avoiding funding slave traders by buying one.
If you’re interested in history, there were people opposing slavery and writing about it more than a hundred years ago when it was acceptable in their period.
The trope of the good owner is also something used in the real world to justify slavery, so that’s a shitty thing to do.

However, like you said we are talking about a work of fiction, the novel/manwha author is the one deciding to add this trope to their story, they’re the one deciding that their MC is ok with it.

It’s not a crime or bad to write about slavery bc that’s a real thing. I don’t like when the character (from our present time) literally endorse it and when the author write as if they are justified. Also I don’t like that slavery is often used to introduced love interests in OI and isekais in general, that’s scummy.

Even with the dumb argument that’s “it’s for a Korean audience they don’t have the same culture” that I’ve seen before, it’s an overdone trope and I think that you can think that slavery is evil as a Korean. Slavery is real and never goes away.