I posted this quote once before, but it seems appropriate to the discussion going on about whether the killing of Bin Laden is not simply justifiable but if it—and other "targeted assassinations"—are morally and ethically and even philosophically and psychologically sound:
"I and the public know
What all school children learn,
Those to whom evil is done
Do evil in return."
—W. H. Auden
(And I would say a large segment, perhaps a majority, of "the public" may no longer "know" this, nor all "chiildren learn" this anymore.)