After initially being skeptical and disliking him for libertarian leaning political reasons, I've come around to wondering if John Maynard Keynes might have been even more right than we have imagined.

Slave labor is kind of an extreme case of the paradox of thrift. Slaves have no disposable capital and they flood the labor market down to zero. Slavery is like a permanent deflationary spiral. There is just no reason to innovate or invest in anything except conquest and luxuries, which describes most ancient cultures well.

Had the Greeks or Romans abolished slavery and set a minimum wage we might be flying to Proxima Centauri in a fusion rocket starship by now.