I look at the death penalty from an esoteric Christian/Anthroposophist perspective. What happens when you choose to just eliminate someone because they did something wrong? Their soul just reincarnates. You are not preventing that being from incarnating again and undergoing the same process and mistakes in a future life. You have done nothing except kick the can down the road and added another wound to their soul by murdering them instead of touching their heart.
In order for evil to no longer exist we have to transubstantiate it, we have to transform it within ourselves and within the world. We have to rehabilitate and heal and learn how to do that with ourselves and others. As long as someone is alive there is an opportunity for them to grow. What do you think you're on this Earth for? Are we here to become more spiritual and grow alike to the Angelic mind and become redeemers of ourselves and others through our knowledge and love of Christ? The only thing that opens hearts is love. It doesn't matter who you are, where you are or what you've done. You are to be loved.
As a culture we don't know what to do with people who are different and we don't know what to do with people who are suffering. Christianity has just become another set of Pharasaic laws instead of something that has sunk into our hearts and this is how you get things like the modern prison system which breeds extremism. These people that operate on such a low level of consciousness where they can only exist in a predator/prey relationship should be sectioned off and undergo a rehabilitation process. Where is the question of rehabilitation in a modern prison system where they are at risk of sexual assault and extortion and violence? What is happening to their souls when they undergo this trauma and how will they look at as humans when they get out?
The death penalty is murder of suffering humans.