Is your belief based in something? You say "shouldn't be able to..." but, like, why not? To convince anyone else of it you'd have to agree on the framework in which states are and aren't allowed to do things.

I think for most people the intuition is something like: the state is there to protect people (in principle at least); when someone is sufficiently dangerous to others they forfeit this right and it becomes just about protecting others from them; whereupon 'vengeance' is basically permitted against them, but then this is also delegated to the state to deter people from doing it individually because that's destabilizing, hence a death penalty.

Seems pretty natural to me unless you happen to have an infinite negative weight assigned to killing someone, which I do not. I mean, I have a large negative one, but it's not infinite. (Maybe yours is, perhaps from the catholic upbringing, which is why this doesn't make sense?)

(No idea what the neighbor thing has to do it; obviously nobody is arguing that neighbors should be (legally) able to kill anyone.)

>outside of war

What was this murder, if not a one-woman civil war?

>Do you want your neighbors to be able to kill you?

My neighbors are always inherently capable of starting that one-man civil war with me, even when locked inside institutions specifically meant to prevent that.

Indeed, the law in the country we're talking about is very explicit about being able to own the tools to wage that civil war as a direct consequence of this fact.

Hiding from that reality has never worked for any other group; why do you think it's going to work for you?

I don't know why you make an exception for war but not the judicial death penalty.