Question: reasons why death penalty should be not allowed?
Answer: You can't take it back. The death penalty is irreversible. ... 
It doesn't deter criminals. There is no credible evidence that the death penalty deters crime more effectively than a prison term. ... 
There's no 'humane' way to kill. ... 
It makes a public spectacle of an individual's death. ... 
The death penalty is disappearing.