You get rid of the possibility that this particular man would not kill again - but at the price of causing other people to become killers, and in a sense requiring that the whole community become killers. And in the certainty, as you have yourself said, that some of the people who get killed by the agents of the community will in fact be innocent.

But to return to the initial case Fionn brought to our attention - that was a man who waqs at the time of the crime of which he was convicted only 17. Still a child. And as the Amnesty report said about execution of children (including people who were children at the time of their offence) since 1995: "In those six years only the USA (eight; four of them in Texas); Pakistan (one); Democratic Republic of Congo (one); Nigeria (one); and Iran (three), have carried out such executions. "

Very interesting company. To me that means that, however you read it, killing child offenders is pretty unusual on the world stage. And that should surely mean that it is against the constitution of the USA.