Americans love to piss and moan about all the freedoms we supposedly have, but are conspicuously unsatisfied with merely removing said freedoms as punishment for crimes.
Maybe they don't think "freedom" is that important or meaningful
In principle I have no trouble just executing Breivik; his guilt is established beyond doubt, he committed an act of exceptional evil, and he more or less declares to want to do it again (well technically he says he wants to be a "non-violent Nazi" or some such, but that's a contradiction in terms: "oh that Holocaust thing was just brilliant, more of that!" is violent rhetoric).
But Breivik-type case are rare. So rare it's not really worth changing the system over it. There's principle of a thing and the practicalities of it: in principle the death penalty is fine, but practically organizing that in a legal system with zero false positives is very difficult, so it's not really worth it.
Aside from the US, you can also look at post-second world war in Europe, which saw some executions that were rather over the top in hindsight.
If you spend some time in the Nordics, you'd find that most don't think "death penalty is fine in principle" as it goes against many of the principles people there try to live by.
Lets see how true this really is: https://news.ycombinator.com/item?id=39826176 - "Julian Assange granted permission to appeal against extradition to US" - https://www.theguardian.com/media/2024/mar/26/julian-assange...
Other than that killing him would be way to kind.
When the crime is still recorded and even announced, it's considered part of the punishment because jail is deemed not enough. It's how we get sexual offender registry.
So yeah, this perspective really depends.
Where was this?
Among support for the death penalty in the United States, is the fact that some criminals, particularly the serial killer type, have committed crimes so heinous that there is no chance of parole or rehabilitation to return to normal life. When one is burdened with 60 consecutive life sentences, it effectively requires that the state pay to sustain the criminal's life until it comes to an end. If the death penalty were enacted instead, we could both reduce the cost the state (which, in turn, is the tax payers), and reduce the suffering the criminal must endure for his crimes.
If you'd like to take the afterlife into account, the "sends the person to eternal torment in hell" sounds like a particular theology not backed up by the Bible, the typical standard in American thinking. That verges way too much on passing ultimate judgment, which is itself reserved for God alone. Perhaps some people believe it. I don't (and I am religious).
It is also supported because it can be used as a self-defence mechanism.
We take it for granted that when we lock up 'really' dangerous people they will be safely away from society, but that kind of infrastructure is a fairly recent phenomena in human history. Prison breaks/escapes still happen:
* https://en.wikipedia.org/wiki/List_of_prison_escapes#2022_–_...
Not only from a building-prisoners perspective, but also from an excess-resources point of view: through most of human history, suggesting using society's surplus—which probably wasn't there—to feed someone 'evil' while everyone else had to work away would have seemed very unfair.
If a single individual has the right to self-defence against an attacker, and a ("small") group of individuals have the same right (e.g., a bunch of folks worshipping in a temple, mosque, church), then wouldn't a "large" group of individuals (e.g., society) have a right to protect themselves from an attacker?
With regards to "hell": someone, while waiting on death row, many repent of their actions and try to find redemption, but still be executed from a legal point of view:
I don't think so. Sin is a sin, crime is a crime, no matter person is dead it alive.