A life for a life...
I'm going to relate an example from my own personal experience.
My aunt and her husband were tortured for several days by two guys who broke into their appartment. And then they were killed.
Do I want the inhumane animals (I have no reservations using the word because, like it or not, we all are) to be hanged, gassed, burned in a pit or otherwise disposed of?
Here's the crunch.
I. Don't. Care.
My aunt is dead and no amount of pain a state executioner or a blood-thirsty mob or a fiesty cell-mate will inflict on these guys will bring her back or make me feel better.
I do definitely want these people behind bars for life, isolated, so that they can never do what they did to anyone else.
Murder is murder. The person who has commited murder is no more or less evil if they killed a man, woman or a baby. Once you've crossed that line there's no going back, no redeeming yourself. But as tempting as it is to suggest that the person who crosses that line becomes somehow inhuman, they do not. They are indeed, still, human. Terrifying, disgusting, appaling - yes, but not inhuman.
After all, only human beings have the capacity to kill AND torture their young for reasons of emotional nature. Am I mistaken or is there no precedent in the animal kingdom for this type of behavior? Human beings are a unique and in some ways (such as this one) highly flawed species. So do we really have the right to pass life and death judgements?