Well, yes, retro. I certainly wouldn't claim that humans are "civilised" as a species. Although we should keep trying. I don't see "mental health" as a label... that is a little ignorant and lazy, as there is a difference (in my view) between people who can or can't control what they do.
While I am not 100% for Capital punishment, I don't see how anybody can say it isn't a deterrent. If you are dead, you can't commit a crime. If the idea is to dissuade other people, then I would say that is really uncivilised, to punish someone in order to change somebody else's behaviour.
Some criminals do consider penalties first, and some don't. But also, if somebody is only ever going to be a danger to society, while alive... is there a positive, to anybody (including them) in keeping them alive?