many people are meant to be slaves is also a fact -- it is not like everyone is gifted cerebrally, or even blessed to be in an environment where, by the time they are adults, have been shown a good formula for life; so consequently a section of the society is destined to be just slaves, it just needs the presence of a manipulator.
Aristotle, being an endless questioning guy he was, might have figured this out, although i'm not sure.
I think you're committing a naturalistic fallacy, and I don't agree at all that people are ever meant to be slaves.
The most I can agree to is that "some humans are born into slavery due to chance". This is factual. That people are meant to be slaves is not a fact. Perhaps we have a language barrier here.
I've no disagreements with your position or moral principles. But spherical cow is different from reality.