Just what occurred to me as a possible solution to make death painful, but also make doing another player in risky enough to be a disincentive to doing it w/o good cause...
ex-Gooserider
Except we're trying to simulate AnCap society in the real world, not in a perfect world where murderers are frozen in place for half an hour.
Default behaviour is to name the deceased, the cause, and if there is one, the killer.
This seems to be more than sufficient. If we want to simulate real life a little more closely, we could remove the killer notification, Or we can leave it in to help nip killing sprees in the bud. Personally, I'd rather leave it in, so people could use the chat to hash out what happened.
You can, in MC, build a prison from which a player can't escape until you let them out, provided that you can force them to surrender their tools.
I agree that there should be no /ban command for dealing with regular miscreants. To give it to a person would make them god. To give it to everybody would make things too easy. No society could survive if it were *that* easy to kill people. Ban should only happen when a player kills another or dies due to environmental hazards. I can see maybe a small number of respawns for environmental deaths. Call this 'childhood'.
Biggest issue with no /ban that I see is the ease by which a player can set off a server-freezing trap. Infinite chickens or melons are always fun. When this happens, it becomes impossible to step in and kill a person by conventional means. If it's stated up front that such things result in perma-ban and the threat is always carried out, this could be considered the conditions of the universe. Alternately, this could be an endpoint for the experiment; one of the triggers to say "This is how long run X lasted before society fell apart."
Ultimately, the biggest problem is that in real life, a person has only one life to give for themselves. Barring religious belief, of course, but a true belief is a hard thing to have in this world. However, in MC, the penalties are much lower. If you're a dick on server A and get banned, you can hop right on to one of a hundred more servers. Maybe they're not quite as good, but it's a fairly small price. So, with an assurance of an 'afterlife', it becomes much easier to have the MC equivalent of suicide bombers: Those who get fulfillment from destroying the lives and works of others in the sure knowledge that when they leave this life, they will be reincarnated and able to do it all over again. A server with the avowed purpose of running such an experiment, and a clear statement that there is no banning or reverting, would be a magnet for griefers. If MC had an overarching method for completely banning people once they'd been banned from, say, 4 or 5 reputable servers, this might work. But as is, it'll be grief city and the honest players will never be able to get off of the ground.