The big problem I have with Armok's theory, is it assumes you have the ability to stop even one death if you dedicated your life to saving them. And that by dedicating your life to saving life you couldn't unintentionally do more harm than good.
I mean, seriously. What are you constituting as saving a life? Feeding a homeless guy for a week? I mean, you can't know if he or she would have lived or died without that food. But you can guess. What if you spend every penny you own buying food for the for lots of homeless people!? Statisticly you have to save someone from dieing then! Shit, now you're out of money. I hope none of those guys grew too dependent on your steady source of food, because that would be like you where starving them.
Maybe that route is too indirect. How about you just buy a stun gun and patrol the streets? Superhero style? Yeah. Stopping any crimes you come across. If you get lucky, and happen to find yourself in New York or Detroit, you might find a crime going on. You can't really stop gang violence, those guys move in armed groups, and you'd be forced to take them all down non lethally. Not likely. Maybe if your lucky you can stop a mugging without you, the criminal, or the victim dying.
Hell, just throw your money into a charity. Course, there is no gaurentee that your money would directly go to something that would save a life. You might buy some kid new shoes, kind of nice. You might pay for the new camera for their advertising. Huh.. Well you can't just say that by donating your saving lives. If that was the case, participating in any economy at all would be saving millions of lives.
These are some vague examples, I'll edit things later to be clearer.