I don't necessarily have a problem with using inmate labor if the prisons are a part of a government owned and operated penal system, if the object is rehabilitation, and if any revenues coming from the inmates' labor is used only for the operating costs of the prison.

But I do have a problem with prisons being operated for profit and using the labor of the inmates as a part of the profit making apparatus. This sort of thing is ripe for abuse, and smacks of slave labor.