That used to be my attitude when folks would argue against the death penalty with the question, "What if an innocent person was executed by mistake?" I used to think this when hearing or reading about some poor guy killed under suspicious circumstances by a law enforcement functionary.
My thinking has changed quite a bit in the last few years. I am a christian and believe a cogent defense for the death penalty can be made from the bible. But the problem as I see it is a corrupt and flawed state doing the executing.
Actually the whole criminal justice system in the U.S. is fatally flawed because its emphasis is on rehabilitation when it should be based on restitution. This is precisely why I have no problem with the death penalty in principle. If one takes a life then one's life is forfeit. But I have real problems with the way it is administered by the state.