I used to be for the death penalty, but I have come to believe it does more harm than good because:
Innocent people are sometimes wrongfully convicted.
The death penalty is often not carried out, leaving the convicted and the families of their victims in extended limbo.
They don't seem to know how to put people to death without making them suffer.
It costs more to put someone to death than to keep them incarcerated.
I would be fine with keeping the death penalty if it were reserved for very, very unusual cases where the evidence was overwhelming, where the crime was extremely callous and violent and where the method used to execute was without pain or suffering and if all cases were fast tracked through the system, taking no longer than two years. This would be for people like Ted Bundy and the Aurora theater shooter.
I believe the death penalty is a holdover from a time when society was more primitive and lifetime incarceration was difficult and cruel to the incarcerated. In this time it serves no real purpose, it doesn't reduce or prevent crime and it seldom brings closure to the family of the victims. It also should not be decided state by state, what we have now is a patchwork of laws that vary considerably from state to state. Death penalty cases, if we must have them, should be decided on a federal level.