When society counters killing with more killing, it really reduces society to the level of the criminals it is trying to condemn. I would think life without any possibility of parole would be acceptable in that circumstance. On a personal level its not very gratifying, but it does get the perpetrators off the streets and that's what the main intent of the system is.
Besides that, the death penalty is just about the only punishment that is un-reversable. Innocent people have been killed by the States, just the possibility of that happening at all makes the case against the death penalty in my mind. According to the leading authority on this subject, Dr. Wik E. Pedia, at least 15 people have been wrongly executed in the US since 1992.
