In my line of work one tends to make a lot of use of a certain device known in the trade as a "thought experiment". I suspect that the popularity of this device among some philosophers is due to a kind of science envy, but I suppose there's no use in speculating about motives. In general I tend to think that "thought experiments" are a waste of time, telling us nothing of any importance and only very rarely having any philosophical interest. However, sometimes they can shed a little light on our values, and in that sense they can, in very rare instances, be intriguing.
There's one in particular that comes up in discussions of ethical theory that I've been thinking about for a while. It's a very old and very simple one. We're to imagine a man hurrying to a job interview in his very best--and only--business suit. The job is such that he simply will not get it if he is either late for his interview or not neatly dressed, and he desperately wants the job, because the one he has now is neither personally fulfilling to him nor financially rewarding, though he is able to survive with it. On his way to the interview he is hurrying through a public square that is empty except for one other person: a two-year old toddler is playing by himself next to a public fountain. As the man hurries by he looks around for the toddler's parents, but there is literally no one else to be seen anywhere. He watches as the toddler climbs into the fountain and then proceeds to fall face-down in the water. It becomes clear that the child is drowning, but the man is still far enough away from his interview that there is no way that he can help the child without both ruining his only suit and making himself late for the interview.
This thought experiment is supposed to trigger an intuition, namely, the intuition that if the man does nothing to help the child then his values are skewed--he has put a certain level of material satisfaction above the life of another human being. In fact, some people would say that if the man does nothing to help the child then he will be morally responsible if that child should happen to drown. Others argue that (a) it's not his child, (b) the child isn't dead yet, and (c) the man can't be morally responsible for an act that he did not initiate himself. The purpose of the thought experiment (to the extent that thought experiments can be said to have purposes), I guess, is to get people who subscribe to these different views to start arguing with each other in front of the rest of the class so the teacher can sit back and get paid for doing nothing.
My own intuitions about this case track rather closely with the former set of considerations. We often hold people responsible for undesireable things that happen due to neglect of one kind or another, and that is what this case appears to be. The man, in failing to help a person who clearly needs help, neglects his duty by failing to help when he can. That the child is not his is not relevant, since the same duty would exist if the person drowning were an unrelated adult. The argument that he will lose his chance at the job is specious, since the story as we have it gives us no reason to believe that he needs that job more than the child needs his life, or that the man will have no other chances at job security, while a dead child has no more chances at living.
To make this position stick, though, one needs more than a naked intuition. In particular, one needs an argument to show that there is a moral responsibility to help others who cannot help themselves. Such arguments do exist, but they are not without difficulties of one sort or another. Here is one that has fewer difficulties than most.
1. All human beings are morally equal
This is not as obvious as some people think it is, but it is more obvious than some others think it is. Think about what it means to say something like "X is a human being." If you want to make the claim that some object, X, is a human being, you need to have some idea of what it means to be a human being, that is, you need to have something in mind that will establish something as a human being rather than as something else. Everybody has some such set of necessary and sufficient conditions, whether they think they do or not. Unless you believe that there is some such set of necessary and sufficient conditions, you are committed to saying that there is no real difference between a human being and, say, a fire hydrant. There are philosophers out there who commit themselves to such things, but they aren't worth taking seriously. They mostly work at places like Princeton.
For the purposes of this argument, it doesn't actually matter what you take the necessary and sufficient conditions for being a human being are. You might agree with Aristotle that a human being is a "rational animal"; or you might think that all human beings share a certain genetic lineage; or you might think that being a human being means never having to say you're sorry. Whatever condition you stipulate, however, will be definitive: either X meets the criteria or it does not. If it does, then it is a human being; if it does not, then it is not a human being. This means that there is no such thing as an entity that is more human or less human than another similar entity. There are no "degrees" of humanity.
The upshot of this is that there is no rationally compelling reason to treat one human being differently than another on the grounds of their status as human beings. Obviously we sometimes treat different human beings differently on other grounds: we put criminals in jail, for example, but not innocent persons, we make children live at home until they reach a certain age even if they might prefer to run away, and we do not necessarily take the rantings of a madman at face value. But these differences, real though they are, do not make human beings fundamentally different kinds of things. A criminal human being is still fully human, as is a child or a madman.
This is important because the essence of morality is the giving and assessing of reasons for acting one way rather than another relative to other human beings. We do not bother to give reasons when our actions do not affect another person: I don't need to justify my preference for Bach over INXS, nor do I expect such justifications from others. We may not approve of another person's preference for Dewar's over The Macallan, but we cannot reasonably demand that they justify their preference on pain of compelling them to act otherwise. We only demand reasons when the failure to give an adequate reason will result in punishment.
Nor can we demand a reason if we apply different standards of reasoning to different persons. It would be impossible for one person to give a justification to another if the one person subscribed to different standards of rationality than the other. Moral reasoning requires that the same logical standards apply to everyone involved. (For this reason, Aristotle's necessary and sufficient conditions on being a human being are rather attractive.)
So we cannot treat one human being differently than another unless we can give reasons that are rationally compelling. To act otherwise would be, in a sense, to act irrationally, since there is no rationally compelling reason to treat any one person different from any other in the absence of a justification.
2. Anyone may vindicate a moral right, whether his own or those of another
So it is because all human beings are the same kind of thing that it is necessary to give some reason for treating one differently than another, and that reason had better be a good one. That is, it had better be a reason that would justify treating you exactly the way you are proposing treating the other guy. If you want to put someone into jail because he stole your money, you had better be prepared to acquiesce in going to jail yourself if you steal someone else's money. If you want to hold another human being as a slave, then you had better admit that you would not mind being held as a slave yourself. If you cannot make that admission, then you have no reason to hold anyone else as a slave. As it happens, nobody can make such an admission. If you actually want to be a "slave", all that means is that you are not really a slave at all, but some sort of weird "volunteer" servant. If you do not want to be held as a slave, then you have no excuse for holding anyone else as a slave against their will either, since they do not differ from you in any way that is relevant to the question of being held as a slave.
If you want to kill somebody, you had better be prepared to let others kill you when the same conditions are present. Now, who on earth would ever be prepared to let themselves be killed for any reason? If someone were trying to kill me, I would protect myself. And most people would be prepared to let me. I would be justified in protecting my life, because the madman has no reason to take my life. But what if I could not protect myself? Suppose I am locked in a room with a madman and an ex-army ranger. The madman is intent on killing me, and doesn't even notice the ex-ranger. The madman, let's say, has a knife, and keeps coming at me. He gets in a few jabs and manages to cripple me in such a way that I am lying helpless on the floor. Now the madman is going to finish me off, and there's nothing I can do to stop him. But he's a puny little guy, and the ex-ranger could easily disarm him and tie him up with his shirt. Would the ex-ranger be justified in protecting me in this way? Would it be morally right for him to restrain the madman and prevent him from killing me? It is difficult to imagine what could possibly be morally wrong in his doing such a thing.
So, if I have a right, say, to protect my life, then surely another person would be justified in protecting that right for me when I am unable to vindicate my own rights for some reason.
But suppose we return to the drowning child scenario. Sure, the man on his way to the job interview would be justified if he did save that child--the question was not about that. The question was, would he be acting unjustly if he failed to protect the child. Would the ex-ranger be acting unjustly if he failed to come to my help?
3. We have a duty to vindicate the rights of those who cannot vindicate their own rights
The most controversial part of the argument is also the most important. My justification in vindicating the right of another lies in the importance of that right being vindicated: if I act to vindicate a right merely because it pleases me to do so, then my act is not rationally motivated--it is not prompted by the process of giving a rational justification grounded in the equality of the person qua human being. If, however, I act because it seems the reasonable thing to do, if I act because my reason tells me that it is what I must do because I would want another to do the same for me were the roles reversed, then my act of vindication is no longer merely a case of the satisfaction of some arbitrary desire that I happen to have at that moment. But if I can apply reason to this situation to show that it is right to vindicate this right here and now, the same reasons would show that it is always right to act in that way. And if it is always right to act in that way because the logic of morality justifies acting in that way, then it would be wrong to fail to act in that way.
So if I am hurrying to a job interview and I see someone drowning, if I have good reason to believe that the person will die unless I help him, and if I also have good reason to believe that I will not be risking my own life in helping him, then I not only am permitted to help him, I have a moral obligation to help him.
Thomas Merton, famously, recounted the story of the Dutch resistance to the Nazi oppression. It was a non-violent resistance in which many lives, arguably, were saved. But opponents of Mertin cannot help but wonder whether the pacifist resistance would have had any long term effect for the good in the absence of military resistance. That is, you can resist peacefully for just so long in the face of an aggressor like that: in the end, the mercilessness of the enemy will overwhelm you. Passivity did not save the Jews, and it is probably a fluke that the Dutch were able to save as many as they did. If the Allies had chosen to continue resisting the Nazis with words only, one wonders what we would think of them today, in light of what we now know was going on in the camps. Would we still admire them, knowing that they stood idly by while millions were murdered? If we have a duty to protect innocent life, we may also have a duty to use compelling force, if compelling force is the only means available to us for bringing an end to the injustice. But this is controversial, since it is not always obvious when force is required and when it isn't.
We tend to think of the Allied military response to Nazi aggression as justified. If we hear accounts of resistance attacks on Nazi installations, we feel that they, too, were justified. If someone were to try to liberate a concentration camp by violent means, we might very well think that they were justified. We tend not to think that people who blow up abortion clinics are justified, however, so we may not always apply our principles in a consistent way. But that we must have principles, and that we must apply them consistently, is quite clear.
The war in Iraq, like the war in Vietnam, has proven to be a challenge to our principles. Are situations like these cases where we have a duty to vindicate the rights of those who cannot act to vindicate their own rights? If so, is military action our only means of giving aid? If so, what criteria do we apply to measure our success in such endeavors?