There is another problem: escalation. If there's the death penalty, once you have comitted the vrime you have nothing to lose but all to gain by commiting more, e.g. by killing all witnesses, killing the rape victim who could identify you etc. Yes, some murderers would do that anyway, but not all.
Also. no one adressed my main point.
There is some misunderstanding. I (and i think the others who are for death penalty here too) do not think that there must be only one punishment for a capital crimes - death penalty. Same type of crime can get different types of punishment, depending on circumstances in which crime get done. That rules out your premise about escalation. If someone murders other person in selfdefense, he does not need to kill all witnesses of that
If someone murders one or more persons in one instance, i do not see any reason for that person to be sentenced to death automaticaly. But if that kind of crimes get repeated several times by same offender, then there is some problem which can not be resolved by imprisonment only. The crimes like murder, rape etc. can be commited (and are usually done) in the prison too, so putting multiple offenders of capital crimes in prison does not keep them safe from not commiting them again.
Keeping that kind of person in isolation for a lifetime is a
1. denying his/hers rights on basic human rights for a rest of its life, in which case i can see that only as a much cruel sentence then death penalty - to say the truth i see that as a unnecesary cruelty, some kind of revenge of society, and as i said laws are not created for revenging the victims, but keeping society safe
2. denying the option of rehabilitation of that person - same as with the enforcing of death penalty
3. technicaly problematic, needs to much of investment of society in something from start unproductive - special prison facilities, guards, food, clothes, medical expenses etc.
From your first post i got impression that your main point is:
"But the decision of whether someone is allowed to live or must die mustn't be given to anyone. I would not trust any judge or gremium with the power over life and death. It is not the decision of one human to make over another."
Well, that would be fine point for a perfect society, but unfortunately:
- someone who murders other person, already decided over victims life or death, and done that by himself only
- someone who distributes narcotics already decided in some way about life or death of his buyers, and again he himself was aware of that from the start
- rulling politicians who decide that someone is dangerous for their goals can sentence them to death by using drones, snipers or even wars to do that, and they decided over human lifes by themselves, out of judicial system of the society
- food producers who deliberately use ingredients dangerous for life or health at least, decide over lifes/health of others too
- pharmaceutical companys put financial gain over lifes or health of other humans, etc. etc.
So, in reality we live in world where plenty of people more or less deliberately endangers the lives of others, even to the level of deciding over their lives and deaths (murderer does not always know personaly his victims - for example terrorists do not choose all of victims of their act), and for that the society did not entitled them with any right (in meaning of law).
On the other side, we have judges.
Judge is the person who in the name of the society, by the laws of society gives apropriate sentence (by his opinion). It should be impartial person, respect his law boundaries when deciding etc. etc. In reality they can be corrupted, have personal interests in some cases or in some cases could be just dumb persons who got that job god knows how. But what differs them from others persons who decide of someones life or death, is that the SOCIETY delegated some trust into them and their doing. So, in this imperfect world, they are the ones who should be trusted for such kind of decision, and even for death penalty.
I suggested one measure in first post for at least keeping them from too much abusing of their power.
So, as much imperfect the solution is accepting the judges as someone who can decide over someones life or death, for now society does not have better.
And BTW, what Gandalf said in your first post is nice, if we exclude the fact that he murdered (or at least killed ) thousands of persons (humans, orcs, demons and others) and with that he effectively decided over their life and death, during his "life" and in the process of gaining his wisdom. Someone can say it was selfdefense or defending others, but even that must have some boundaries. If not, even for the Hitler could be said that he was only defending the Germans from others .
In the end, some facts from life about allowing someone to decide over the persons life or death that talks in your favor Partysan In my country will be soon approved law which allows medical doctors to end the life of patient which can not be healed. We do not have death penalty as a crime punishment, we do not approve euthanasia by our laws, and yet there will be some medical doctors who could terminate the life of their patients even against their wishes, using only their medical opinion as a reason!!! Moronic law, even against our constitution, but it will be approved.
That law is just badly translated law our politicians got from our friends from EU. That proves only that even democracy is imperfect solution for organising human societys.