A chance to change, sure. But it would be a mistake to pretend it’s not also a chance to kill again. And it turns out people actually can’t change, meaningfully, without remorse for their past deeds— And you can’t ever actually know whether they feel that. Mercy feels very good until you realize ten years later how much pain you could have avoided otherwise.

Also, you’re presenting a false dichotomy between “Set them loose on the world” versus “Isolation and torture for the rest of their life”.