Could you really have done so? Its easy enough to write on a forum in anger isn't it, but could you really have done so?
Without a shadow of a doubt! I know what I am capable of, and killing someone like that in those circumstances would be well within my remit. I would want to be a combatant in time of war!
In a time of war if faced with someone who was about to kill then I would try to defend myself (or others) or try to get out of danger. If that meant having to kill then I would probably (like most of us) go off basic human survival instincts for that time. I would not take any pleasure in killing another though - I would try another way if one were possible rather than kill.
I wonder if those who think Bin Laden should have had mercy would have felt so kindly disposed towards him if one of their rellies had been killed on 9/11?
The situation with BL is rather different - and I would not call it showing 'mercy'.
To choose a stance as JJ posted (part of it is Martin Luther Kings words) well some might call that a weakness. Do those that believe it to be a weakness not think that anger and sorrow is still felt by those striving for peace, when innocent people are murdered?
It takes a lot of strength not to seek revenge!