In the same essay, Thomson also tells the story of the violinist newly connected to you: "You wake up in the morning and find yourself back to back in bed with an unconscious violinist. A famous unconscious violinist. He has been found to have a fatal kidney ailment, and the Society of Music Lovers has canvassed all the available medical records and found that you alone have the right blood type to help. They have therefore kidnapped you, and last night the violinist's circulatory system was plugged into yours, so that your kidneys can be used to extract poisons from his blood as well as your own." In nine months the violinist will have recovered from his ailment and can then be safely unplugged from you. But if you unplug him much earlier, then he will surely die. Does this do it? Do you have the intuition that it would be permissible for your to unplug right away?

You slide too easily from "ought to be legal" (which is what Clinton was saying) to "is morally permissible" to "is not regrettable". Neither of these transitions is valid. The problem with each transition can best be brought out by example. There are strong reasons for insisting that the expression of beliefs about scientific matters should be legal even when these beliefs are idiotic. So we strongly believe that people should be legally free to express the beliefs that there is no global warming, that global warming is not caused by human beings, that the members of certain races have inferior intelligence, that women have less native ability to deal with numbers, and so on. Expressing such beliefs is hurtful and damaging to social relations, and expressing such beliefs carelessly is therefore morally wrong/impermissible, at least in many cases -- and ought nevertheless not be criminalized. Similarly, it is often morally wrong to lie to your spouse; and yet we have good reason not to outlaw such...

Kant's contradiction in the will test suggests what you say it suggests only on the assumption that, as a rational agent, one necessarily wills one's own existence. Most human beings are happy to be alive, but it does not follow from this that any human (let alone any rational) being must will its own existence. Indeed, some philosophers have argued that, by giving birth to them, their parents violated their rights. So I think the best way to reject the Kantian argument you are suspicious about is to reject its premise that a rational being necessarily wills its own existence. Something Kant did think rational beings necessarily will is the continued existence of rational life. Using this premise instead, we might get a moral rule against abortion when the survival of the human race hangs in the balance. Suppose rational beings found themselves in a world where, if they all took themselves to be permitted to act on the maxim to have an abortion whenever doing so promises a more pleasant life,...

What does potential count for? I don't think there is a general answer here. One important variable concerns the relation between the potential time-slice person who never came to be and the entity whose development into that time-slice person was disturbed. When these two are closely related, then potential may count for a lot. When you prevent a very talented and highly trained athlete from traveling to the Olympics, then you deprive this person of her chance of a medal; and this seems quite serious because here the person prevented and the person who would have competed are very closely related (the same mature person a few days apart). But suppose the opportunity to compete in the Olympics was closed off much earlier by the parents who sent the first-grader to the chess club rather than to the gymnastics club, so that she becomes as chess lover rather than a gymnastics lover. While the world may have lost a great gymnast, this is not a substantial loss for her (because gymnastics never came to mean...

Agreed, the bumper sticker has very little persuasive appeal to those it purports to be addressing. But something could be said against your more general point, as follows. Suppose someone believes that abortion is morally (roughly) on a par with infanticide and murder, and also that infanticide and murder are terrible crimes that ought to be criminalized and punished severely. Would it be incoherent for such a person also to hold that the criminal law should not interfere with any woman's decision about whether to have an abortion or not? One could hold these two views together -- in fact, Mario Cuomo held them together when he was governor of New York State. One could rationalize the combination like this: "I am convinced that abortion is murder. But the grounds of my conviction are rooted in a religion that many of my fellow citizens do not share. In fact, my country is deeply divided on the issue of abortion, with many reasonable persons on either side. Under such circumstances, it would...

By the same reasoning, your mother would have done a terrible thing to you if she had abstained from sex on this occasions or if she had insisted that your father use birth control. Such conduct, too, would have denied a good life to a person in the future. I assume that you would not want to classify such conduct as worse than murder, but rather as perfectly permissible -- even though sometimes, when you use birth control, a person who otherwise would have come to exist will not. The problem with your analogy is this: In the case of murder, there is a person who is harmed, a person who is deprived of further years of life, prevented from realizing her plans, projects, and ambitions. In the case of abstention or birth control, by contrast, there is no person who is harmed, no person whose life is cut short, no person disabled from realizing her plans, projects, and ambitions. Murder harms an existing person, birth control merely prevents the coming into existence of a person. This explains...