“The person simply deserves…
“The person simply deserves to be punished in the criminal legal system regardless of the effect on restraint and deterrence.”
Again, whether or not a person deserves X and whether or not we can legitimately give her X are two different questions. I have very little in the way of confident positive beliefs about what murderers do or don’t deserve, but I am quite sure that even if a murderer does deserve punishment we can’t rightfully inflict that on him or her against her or his will. (Again, because as a libertarian I condemn all forms of violence not in defense of self or others, and we’ve stipulated that the punishment in question serves no defensive purpose. If you intend to show that we can rightfully inflict punishment on someone who deserves it, against that person’s will, you’ll have to give reasons to think not only that they do deserve it, but also that the ordinary ban on aggressive violence is repealed in the case of convicted criminals.)
“What kind of restitution are we talking about for murder?”
I mean damages for wrongful death, payable to the victim’s estate (since the victim is dead). The sort of thing that you could today gain through a wrongful death suit (or perhaps more, since a system that exclusively depended on restitution might tends towards higher restitution than one in which restitution is thought of as something taken in addition to punishment).
“There are some crimes that are so heinous, that yes, it really wouldn’t bother me — that is, were I the master civil magistrate, I would vet such a punishment — but I’m not sure if the parent murder hypo that we are discussing is one of them.”
But you are sure that killing the murderer (provided that there’s no chance of error, etc. etc.) would be a fit punishment?
(As far as the 8th Amendment goes, well, let’s set that aside. The 8th Amendment can be changed or repealed if it serves the aims of justice to do so.)