In the long run, such tragedies are not avoidable. Sooner or later something goes wrong and innocent people die, whether you're talking about hunting down terrorists, testing new airplanes, or just driving through an intersection enough times to be the unlucky bastard who's there when someone runs a red light.
Whenever military action is undertaken, no matter how justified, it is all but a mathematical certainty that innocent people will die. All we can do at that point is:
a) Make sure we are justified in taking military action;
b) Do whatever we can to prevent/minimize the death of innocents without unduly jeopardizing the mission;
c) Accept whatever deaths of innocents do occur as the tragic cost of doing business;
d) Don't look back.
Anything else is overthinking, second-guessing, or emotional/political grandstanding.
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This was not a military action it was a (supposedly) well-researched, planned hit that did not have to be made at that moment. And, it was avoidable.