The Undercity is hidden from most of society. Good folks don’t need to see how bad others have it. If someone’s in the Undercity, it’s because they’ve been deemed a non-functional part of society. Some would argue that those living in the Undercity have a debt to pay. Some in the Undercity agree and work towards repaying that debt, even if their methods are unorthodox. They take what’s needed to serve the good people of the surface: kidneys, livers, cybernetics, hearts, you name it. This gives their life a purpose. Just be careful not to be on the wrong side of the blade.