There was once a psychoanalyst who was fond of asking patients this question: "How much is your life worth, in kegs of beer?" The result was usually consternation and the intended focusing of attention. But it is a real question nonetheless. How much is your life worth in dollars? Well, obviously, to you it is worth more than anyone could pay, since without it you would not be around to enjoy the profits.
However, suppose you could save the life of someone you love by giving up your own? This can be a tough decision, but almost everyone is willing to take the question seriously, since it involves a life for a life, not money for a life.
If you win the big lottery, how many lives could you save with the money? Now divide your winnings by that number, and try to tell me that you have not just calculated the monetary value of a human life. I hope you will keep this figure in mind if you do win the big lottery. Again this is not a very threatening question, because it only involves saving lives with money.
Now we get into the hard stuff: are some lives worth more than others? We certainly seem to think so. Through our taxes and public services we will gladly spend hundreds of thousands of dollars to save the life of a child trapped in a well, but we may be reluctant to invest a similar amount to ward off starvation for an entire village of African farmers whose crops have failed due to drought. If you examine the implicit rationale from a biologist's point of view, it seems clear that such priorities are dictated by a combination of sociological [formerly genetic] imperatives ("Family/tribe first!") and what I call Gambler's Economics ("I've got a big investment in this person already, and I'm not going to let it slip away!"). Although none of us are likely to be cheered by this view of our motives, we can probably live with it.
But here is a question that many people can't even entertain: Suppose you could actually trade one life (not your own) for another, or for a dozen others? The classic example is the Cop's Dilemma: a terrorist is holding a room full of people hostage with a bomb, and for a moment he puts down the trigger device to tie his shoelaces; you have a clear shot. Do you take it? The analysis of this situation will almost always be diverted into questions of whether you might be mistaken about the seriousness of the situation, or inventions of "better solutions" that surely must exist. No one wants to face the question head-on, because they probably sense the slippery slope that lies beyond it.
If you are willing to blow away one criminal to save many hostages, how about a more indirect exchange of lives? You are offered a massive amount of money to assassinate a political leader whom you dislike intensely and would just as soon be rid of; with this money you can save that African village.
If your main concern there is with getting caught, let's crank it up a notch: a major drug dealer offers to move his operation out of your city if you will just eliminate the popular politician against whom he has a grudge. No, I don't think it would be a good idea to trust a dealer's word in such things, and I agree that an honest politician might someday do so much good that his or her life would be worth the continued predation of the drug trade; but we are avoiding the issue, aren't we?
My purpose here is not to encourage murder, but to remind you of the "shades of grey" that mark all boundaries between good and evil. Simple pre- and proscriptions may help as guidelines, but they don't let you off the hook for thinking through every important decision. You not only can, but must "put a price on a human life."