Yes, slavery was prevalent in the Greek city-states, and Epaminondas didn't change that, but still the slavery in Lacedemonia was a different beast. Although there was no attempt to portray Helots as non-humans, and they weren't bought and sold, Helots could not expect their children to not be in the same kind of bondage they were in - and so I see parallels to the chattel slavery in the pre-emancipation South. I also see parallels with the proto serfdom of the late Roman empire latifundias - with the exception that that latter was not a type of people being forced to labor (trying to dance around using 'race', a concept that came later, and to our detriment, IMO).