Exploitation is built into human nature, and slavery is just the extension of the natural urge to exploit. Eventually, this will spill over into something else.
The gleaming towers of neon and steel stood proud against the sky. Numberless uniform windows reflected the too-perfect blue sky, giving the view a almost heavenly lightness. Imagine the view pans down, revealing the ugly underbelly of this acheivement. Acrid clouds of pollutants, leaked chemicals and god-knows-what-else partially obscure our view of the rusted, ruined yet somehow functional industrial section. Great machines churn and grind, preforming long-forgotten yet nessacary functions for the gleaming utopia above. Crawling all over this maw to hell are it's outcast maintainers, those cursed to suffer for the metropolis above, thanklessly and ceaselessly. They are those who the dwellers above cast off long ago, leaving them to fend for themselves, feeding off the scraps left unwittingly by they're former brothers. But now, the rich and powerful rely on the services this underclass provides.