There is no evidence to show that capital punishment reduces the level of violent crime in a society. The opposite does have some evidence in its favour. When in the early 19th century the UK reduced the number of capital offences, serious crime reduced. This may have been partly due to the improvement in living conditions rather than as a direct result of changing attitudes to capital punishment.
For me, however, my absolute aversion to it is twofold. I believe that there is an underlying desire for retribution in calls for the restoration of capital punishment in, say, the UK, and retribution should not lie at the moral heart of a society. Secondly, those who are executed are beyond the human processes of redemption, restoration and reconciliation, I am do not believe that we have the moral authority to exclude people from that possibility.
I long for the day when the two superpowers, USA and China, begin to share this view, and take their place in the world not simply as those who control but as those who set an example for others.