Your question is sound - one couldn't. Mind you, blowing away an airliner full of hostages in order to prevent potential damage at the other end would not be a choice I'd care to make.
I think, though, that Holder was being highly disingenuous by referring to those incidents. The question was clearly focusing on the sort of drone attack used so often in Afghanistan and elsewhere. I hope I'm not being entirely paranoid by reading Holder's answer as "In an emergency the President can blow away anyone he likes."
Thank you for your response. There are times when a president must act regardless of the difficulties presented by the choices.