I do genuinely hate that it's a hot take,
But- Eternal Punishment is exclusively evil, and pointless. It causes nothing to become better.
While it is true that I also believe that Vindicative Justice is inherently wrong, it is also true that many people do not understand "Eternal", or "Forever", and many people also do not seem to realize that the reason they want bad people to suffer is not because it solves the problem, but that humanity possesses inherent sadism.
Sadism is not a synonym for evil, even if it is arguably a form of it. Sadism is the desire to cause harm to, see the anguish of, and to enjoy abuse of a victim. Whether or not said victim "Deserves" it or not, Sadism applies if these things are true.
And for most people, sadism is triggered when someone is seen as evil and/or a threat. Sadism is also a very effective vice that turns our stress and creativity into malevolent joy. And what is going to bring that kind of joy more than seeing someone suffer forever?
A thing I believe is that Empathy and Sadism are not nessecarily mutually exclusive but, Empathy forces people to artificially feel connection to people and wish to help others that they are connected to, while reducing any sadistic desire towards them. When you think of "Eternal Torment" do you envision all meaning slowly withering away until the victim loses sentience and is just a ragdoll being thrown around and abused? Because unless you reset them every now and then, they will break and become a non-sentient puppet and there is nothing you can do to stop it. And even before that by suffering they endure will eventually eclipse any suffering they incurred and become inherently more of a bad thing than anything they've ever done.
Am I saying "Bad people shouldn't be punished"? No, I am saying that causing suffering that isn't explicitly nessecary is pointless, evil, and just outright malign. Eternal Torment has no purpose, even if a lesson is learned it doesn't matter because it's endless. Just kill them, there is no point to keeping a threat alive or existant if it stays such, and you even discourage any lessons from being learned by making them resent you and the whole system. While it's ideal to reform bad people into good ones in my opinion, not everyone CAN be redeemed, so instead of torturing them which won't teach them anything, just kill them or re-form them.