Mark CMG said:
When is the treatment of slavery in D&D campaign settings inappropriate, if at all?
I say take a page out of Werner Klemperer's book, he was the actor who played Colonel Klink on Hogan's Heroes, in that the slavers should never be protrayed in a good light and, in the end, they should lose.
Maybe they're idiots, fools, or however you have it, but they're the bad guys and they should be made to look as such.
That said, I think it is a good sign that the DM is concerned, a sensitivity towards your players and something they might be offended by is a good thing.
He or she needs to take the next step and talk with the player, potentially with all of the players, so as to not single out anyone.
They can just point out, "Hey, I've an arc here that touches on sensitive subjects and I just want to make sure everyone is okay with it."
I mean, it happens. I've had games in which I've touched on some nasty subject matter, be it cruel, inhuman, or what not, but I never glorify it. In most of my campaigns the good guys should overcome evil, be it as a player of a good guy, or the GM controlling the forces of evil.
Now, the PCs have to work for it, but rarely would they, or should they, condone something that most consider evil.
But, back on topic, I suggest just raising the topic with the player(s) and let them know that although you don't think it is a problem, they do know that the subject matter (slavery) is a touchy subject and you wanted to make sure it was okay to move forward.