The flip side of that is that an innocent person can not be murdered by an executed felon who has served his sentence and been released .
Course, you don’t have to execute people to achieve that. And also, if you execute the wrong person, then the actual criminal is probably still out there.
I suppose a major consideration is where you think the acceptable level is for a state to kill innocent people by mistake. Lots of people say zero, others think there’s a tolerance level. Once you get into trying to offset innocent executions against potential deterrance of crime and doing some cold equation where one justifies the other, that’s incredibly shaky ground. You can do some fun reductio ad absurdum there.
I’m not sure where I really stand on the morals of execution; but that’s OK because I know exactly where I stand on executing the wrong dude, and that takes care of the whole question.