Aside from the fact that killing is just plain wrong, there will never be a justice system that is 100% reliable. it will never happen. and therefore, you cannot kill people when there is an element of doubt, however small to their guilt.
I'm sure Derek Bentley's family gains no comfort from his conviction being overturned 45 years after he was hung.
We talk of the guildford 4, but what about the birmingham 6, bridgewater 3, m25 3. judith ward.
too many people would have wound up dead because of an unreliable justice system. You can't say sorry to someone once you've killed them.