The reason bad people are sure that horrific prison conditions and rampant executions will "prevent" crime is that those are the only things that would prevent them from committing crimes.
That's why our failure to deal with the parasite class in a definitive manner over the last 50 years has resulted in the collapse of society: without the terror of consequence, morally empty people have no incentive to not rape thousands of children or commit genocide, among other atrocities.