Can someone tell me why prison labour's is wrong?

If I were a very wealthy individual with millions if not billions of dollars and I wanted to build a village or a town or a city, I would setup a contract with wardens of the most overcrowded prisons not just from the United States but all over the world where prisons are overcrowded. I would only have the most muscular and biggest and baddest and strongest male prisoners, have them taught how to build small scale buildings and manufacture resources to build a beautiful village/town/city and the only thing I would give them would be something cheap like mashed potatoes and spring water.
Can someone tell me why prison labour's is wrong?
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