I'll even add to your side of the argument revenge (as you've said), Martyrdome, economics. Here is my point...I am not sure of the deterrent issue...as well, rather we should be bigger than this as a society or not, there is a sense of justice in its "ballanced" nuance in society as a whole...people not directly involved/impacted tend to see "fair" or "ballance" when a killer is killed. I believe that sense of ballance is of equal import to the operation of the justice system. JMHO based on my anecdotal experience.