Well on the moral aspect of things, I don't like the fact that we kill people simply for the self gratification of it all, even if they are the utter scum of the earth. But looking at it from a practical point of view; There isn't much use for a person who spent 20 years in prison for murder and has no hope of rehabilitation and might still pose as a threat to society. It's just a waste of tax payers money. Since they no longer contribute anything to society, you'll probably just be doing them a favor with the death penalty...