You trot out the claim of other deterrents and say taking the life of a murderer is unjust but you offer no alternative, just a lot of left wing pablum.
Go back and read my posts unless you're just trigger-happy. I have offered a number of effective alternatives and valid deterrents.
OK, just for you: effective incarceration itself is a deterrent. Valid reasons for incarceration include restraint (protection of society from dangerous criminals - the #1 job of government), restitution when possible, voluntary rehabilitation, forced productivity to pay for one's stay at the Big House, all of which can serve as added deterrents.