It's absolutely massive when you consider that locking up humans in cages is perhaps not the sort of thing we ought to encourage by making the practice lucrative.

The existence of even a single for-profit prison provides a perverse incentive to put the marginal criminal into a private, profit-generating cage rather than a public, tax-draining, politically-risky rehabilitation or diversion program.

Furthermore, it is an invitation to corruption. Remember the judge that was sending juvenile defendants to a reform camp, often regardless of the merits of their cases, because he was getting kickbacks from the camp?