It's called The Sheriff's Dilemma in philosophy, and it's one of the toughest problems ever...

In the old West, a young girl gets raped and murdered in a small town. The citizens ask for an arrest, and the sheriff delivers. Only: the sheriff knows his suspect is innocent. Riots all over, citizens demanding for the sheriff to hang the suspect. Should the sheriff hang the (innocent) suspect in order to prevent riots with possibly hundreds of dead citizens?

I wouldn't want to be the one to give that order, unless I would be 100% sure that the plane would indeed kill more innocent people when striking its target than there are innocent people on the plane... but you never can be 100% sure...

Is it right to kill innocent people in order to protect innocent people? Do you judge that by how many innocent people are on "either" side? Do you count children twice? Do you count people who have stolen candy in high school less?...