I think crimes, like murder for example, should not be something you are allowed to be “rehabilitated” for. And keeping someone in prison to rot in a cell for life is kind of inhumane. So death penalty is both proactive for the community and a quick relief to the suffering of the criminal.

Laws are a societal contract. They are not set in stone, and can be changed with enough political will. What's stopping me from creating a political party that has the will to create specific laws that make the death penalty applicable to anyone I want to target?

Having the username 'u/jennsnotscary' is now a crime worthy of the death penalty. This is a crime that should not allow the individual to be rehabilitated. Keeping the criminal in prison in a cell for life is inhuman, therefore the death penalty is justified, is both proactive for the community and a quick relief to the suffering of the criminal.