I also have a consistent life ethic, but (if I may pat my own back for a moment) I'm also wise enough to know that keeping murderers alive is not a consistent life ethic. Leaving people alive who deserve to die puts other prisoners at risk (my brother-in-law is a CO, and he is full of stories of things he has seen with his own eyes that would make your blood run cold). Keeping them alive puts innocent CO's at risk (If you've been sentenced to life without the possibility of parole, what else can be done to you if you murder other inmates or CO's? Just tack on another life sentence?). Occasionally prisoners escape and then murder other innocent people while on the run (look it up, it happens more often than you probably think).
In short, it seems easy to say, "I'm just for life. Let's keep killers away from the innocent and that way, we aren't responsible for killing anyone or accidently killing someone who is innocent." Reality doesn't work that way. As Thomas Sowell says, "There are no solutions, only tradeoffs."
By keeping murders alive, the State gets to wash it's hands of direct responsibility for the deaths of guilty people. But when the State decides to keep a murderer alive, doesn't the State at least share in the responsibility for all the people killed by murderers who have been caught and convicted and then kill in prison, or escape and kill, or are released and then kill again?