Amazing.External link →
Those who are in favour of slavery never think that they may be on the wrong side of the whip.
Except OP's slave. She's no hypocrite.
Or they assume they will if they don't do it first. "Enslave or be enslaved" kind of thing.
Especially in the ancient world, tribal societies, etc I can imagine this attitude being pretty widespread - possibly to the point where it's not really remarked upon, the same way we build horrific weapons all the time today.