Hey Veeky Forums, I've been homebrewing a humanless setting for 5e, and I have encountered a problem. When making the tiefling civilization, I intended to make a society of philosophers, clerics, and wizards that also practiced slavery (genasi, inspired by tales of wizards with djinn and elemental servants) with hellenistic, byzantine, persian, arab, and jacksonian american influences. Somehow I ended up with a society that almost entirely revolves around a brutal system of racial slavery, who are also wizards, instead of a society of wizards who also practice slavery.
I wanted each of the races in the setting to have civilizations with a morality and system of values different from modern day, but I know that race-based chattel slavery will be like hanging a "Official Evil Faction: genocide for sweet loot and xp" sign in the minds of your average player. I want to put my players in a strange, foreign setting, where people think and act differently than they do here. I don't want there to be anything they can easily reduce to some cliche to cling to, or re-wage the American Civil War.
Ideas I have so far to take the rougher edges off the tiefling civilization is to make slaves able to purchase their manumission, forbid the separation of families, mandatory emancipation after certain periods of time, different classes of slaves (some nicer than others), or religious traditions that encourage manumitting slaves on holy days.
Is there some way I can make their society less galling to modern eyes? What are some alternate systems of slavery that have existed? What are some protections or rights some civilizations have granted slaves, serfs, bondsmen, and thralls?