In Soviet Union having prisoners do soft labor was called Sharashka. This scales and creates incentives to have more prisoners doing cheap labor.
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If he was being coerced into labour however, which the for-profit prison undoubtedly makes profit from, it’s simply unacceptable; indentured servitude, slavery, call it what you will, it’s bad for society in every way because it allows the ruling class to steal labour from the working class under the guise of “rehabilitation”.