For one thing, the word, "slave" has become verboten in modern American idiom. People who were "slaves" are to be referred to as "enslaved persons," and don't you forget it.
But it's an interesting question. What if a novel were produced in which a character was portrayed as a good and faithful, say, house servant who was an enslaved person. It is conceivable that such a person could have existed, and even that such a person was satisfied with his/her lot in life, all things considered.
While the character might be offensive to someone alive today, there are many analogous characters in fictional (and real) history. What about wives who were happy in what other people considered an abusive relationship? What about a child who was raised by a strict martinet, but was fine with it, even after reaching adulthood? Just because WE think that a person should have been miserable, we don't have the right to eradicate any mention of the person or his condition.
I personally don't understand much of the South's exaltation of their Confederate history. I couldn't believe it when I was assigned to Fort Lee, Virginia, named after a famous Confederate General. Not to get technical, but wasn't he a traitor?