That's exactly what I find disturbing about it. I wouldn't assume the authority to determine the fate of any person for a greater good I can't possibly conceive.
I know myself well enough to know that it's exactly that sort of behaviour that would open the floodgate to my own passions, and I would end up doing monstrous things in the name of justice, or morality, or whatever.
So, for example, would I kill one person to save ten? That's not my duty. Am I in the army? Am I with the police? Nope.
In a position of extreme duress, maybe. In a very personal matter, maybe.
But do I want to live in a society where anybody thinks it's okay to take up the gauntlet and play hero? Hell no. Every idiot thinks they can save the world. Even worse, every genius thinks they can save the world.
I want police officers who do their job and get their asses beat if they behave corruptly, armies who defend the nation and face death penalties if they turn into mercenaries, companies who make a decent product or go completely bankrupt if they make a mess, and politicians who get royally reamed if they slip up. And I want to be treated in that exact same manner when I go to work.
That's the kind of saving the world needs.