Capital punishment - my thoughts

There is an online petition calling for the return of the death penalty in the UK. It's qualified so that it would only apply to those who killed cops and kids, but any reintroduction of the death penalty leads to a slippery slope.

My understanding is that we, living in the UK, live in a civilised society. So where, in a civilised society, is there the place for retribution in our criminal justice system? Because that's what capital punishment is, at the end of the day.

What gives the State the right to choose who is to die, how, and when? How does that make "us" any better than the people capital punishment is purporting to protect us from?

Does capital punishment protect our society from killers? Looking at data from the US, I would say no, it does not.

Acting after the event does not lead to prevention. Put simply, the death penalty does not act as a deterrent. It will not stop people from killing, let alone killing the police or our children.

The notion appears, to me, to appeal to the braying mob baying for blood. 

This is not the measure of a civilised society.