I'm personally for it. And I'm talking about cases where there is 100% evidence.
For example, near where I used to live, there was a small boy who was killed by his mother's boyfriend. She had left her son alone with her boyfriend while she went to run errands. The boyfriend physically abused the little boy (breaking bones all over his body), sexually abused him (left a lot of DNA evidence), and eventually killed the little boy.
I don't believe people like this should be able to live or live comfortably in prison.
And the death penalty might not be an effective deterrent...*BUT* it gets these predators permanently off the planet so they cannot victimize and hurt other people.