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If you want to execute people on the cheap, remove some of the due process and accept that you will occasionally condemn and execute an innocent man.
You assume then that there are no innocent people on death row in US? Hmm there are reports of some being released from time to time which surely tells us this is not true? What about badly done DNA checks as was reported lately? What about few other 'little' shortcomings of US justice systems where it is sometimes better to accept a 'deal' putting one in prison for life than fight an uphill battle with a chance of ending on death row.
"No matter where you go, there you are..." -- Buckaroo Banzai