Correction: You don't think it's enough. I think if they've made their way through the entire justice system and are still cannot be rehabilitated in any way shape or form, there's really no point into keeping them in prison for the rest of their life. It's a waste of our and their time.
I'd say if the act doesn't land me in prison for life, then I am definitely different from the criminal in question. Either way, there's a pretty loving big difference in advocating for the death penalty and actually wanting to straight up kill criminals. What are you smoking to believe otherwise?
The issue i'm trying to address is that judging someone's life as a human is impossible. Humans are flawed by nature and are influenced by personal bias, beliefs, emotions, etc. Those will always get in the way of the final decision, and results in an unfair or unjust taking of someone's life.
Advocating for the death penalty is different from directly carrying out the execution, sure, but as a supporter you are directly leading towards their death. You may not be the one who injects them with lethal poison, but you and other people are allowing it to happen. That's the issue; you can't dehumanize a human under any circumstances. You can't advocate for murder and be against murder.