Those who have read my other posts will know I am not a liberal.
I am strongly against the death penalty.
When deciding the matter of 'what to do with this criminal,' society's primary consideration should be what is best for society, not what is best for the criminal, or what the criminal "deserves."
Life rarely gives us what we deserve. A starving child in Africa may complain, rightly, that he/she does not deserve to die at the age of four. But guess what... that's the universe we live in: cold, unfeeling, unreasoning.
Life is not fair. The goal of civilized society is not to try to make life fair, or even 'as fair as possible.' As a society our goal should be to create an environment conducive to the success and growth of our citizens. So when someone becomes a "criminal" and disrupts our efforts to create or maintain such an environment, the decision on how to handle the matter should not be based on emotion or on some ideal of "justice" which is unobtainable anyway (as soon as the crime was committed, justice has been irreversibly breached; as the tired but true argument goes, killing the murderer won't bring the victim back).
Throughout history many cultures have realized this. If a member of a nomadic tribe was a danger to the success of the group, the worst penalty that could be inflicted was exile. In many cases this no doubt meant death for the solitary individual on his own. But society did not have to expend its own resources in carrying out a punishment, and it rid itself of the threat to its success.
In our current society, the last time I checked the figures, it did indeed cost us more to execute a criminal than to imprison him for life. When it comes to dealing with scumwads, I don't want the drain on society to be a penny over what's necessary.
Add to this the fact that having a death penalty policy will inevitably lead to a certain number of innocents being put to death. Exactly how many innocents is it acceptable to sacrifice in our pursuit of vengeance?
Extending the death penalty to crimes other than murder would be yet another step in the wrong direction.