Imagine you are an observer for an NGO in Darfur and you come across a village where a military commander has lined up fifty people against a wall and is about to execute them because someone from the village fired a shot that killed a soldier last night. You say, “Stop! Only one shot was fired, and thus most of these people are innocent.” The commander looks at you with disdain and hands you a rifle, saying that if you kill one person, he will let the rest go. He warns you not to try anything foolish because his soldiers now have their guns trained on you. Do you fire and save forty-nine lives, thus dirtying your hands, or do you drop the rifle and maintain the integrity of your principles while watching the commander kill fifty people?
(and no, you cannot shoot the commander. This is not an option for this discussion. Your ONLY options are to kill one villager or none at all)