A while ago, in a post on abortion, I had a brief discussion with Jeremy Pierce about the distinction between rights and obligations. Since we are discussing abortion again, I thought now would be a good time to clarify what I mean by this distinction. I will also discuss briefly how this applies to the abortion debate.
First and foremost in this distinction is this: rights belong to the province of public or political morality, whereas obligations belong to the province of private or individual morality. Political morality has to do with the existence and nature of morally appropriate government, what it may and may not do, what people may do to one another, etc. Rights belong to this realm, because it is morally permissible, in terms of political morality, for you or your agent to enforce your (negative) rights against me. If I violate your negative rights, you or your agent (e.g., the government) may punish my transgression. Obligations do not belong to this realm, because it is not morally legitimate for you to force me to fulfill my moral obligations, even my moral obligations as regards you - with the exception, of course, of my obligation to respect your rights.
That paragraph might be a little opaque, so let's take a real example. I believe that the rich have a moral obligation to help the poor, but the poor do not have a right to the assistance of the rich. What this means is that if a rich person fails to use his wealth to help the poor, this is a moral imperfection, i.e., a sin. However, because the poor do not have a right to his assistance, they have no legitimate political grievance against him, and neither they nor the government may justly punish him for his immoral behavior, because this is a matter of personal morality. On the other hand, the poor have a right of self-ownership, which includes a right not to be forcibly enslaved by the rich. If the rich do enslave the poor - literally enslave them, and not merely "exploit" them in the Marxist sense - the rich not only act immorally, but transgress the rights of the poor, and therefore the poor or their agents may justly punish them.
Now, the situation begins to get sticky when individual morality and political morality cover the same area in seemingly contradictory ways. For instance, Christians are commanded to "turn the other cheek" to someone who assaults them (Matthew 5:39), but, according to my (libertarian) political theory, they have a right to exact punishment. What this means is that there is a case in which a person has a right to do something, but an obligation not to exercise that right. This is indeed a little sticky, as I said, but it is not terribly troubling. After all, it is easy to see other similar cases that are more straightforward. For instance, I have a right of free speech, but there are some things that it would be immoral for me to say. So there may be some cases where a person has a right, while at the same time has an obligation not to exercise that right, or perhaps not to enforce that right against those who violate it. No problem.
Now, as to abortion, like I said I just want to sketch how this distinction will apply to the debate, not develop a detailed account of the morality of abortion. I think it is absolutely indisputable that a couple who voluntarily and intentionally brings a child into being has a moral obligation to care for that child and bring it to healthy adulthood insofar as they are able, even from before it is born. I think that, while not as indisputable, this is equally true in cases where the couple did not intend to create a child, but nevertheless does so by engaging in consensual sex. In fact, I think it is probably the case that the parents of a child have such obligations in all cases, even rape and birth-control failure. However, in order to justify illegalizing abortion (or even exposure of infants!), it is not sufficient that the parents have such obligations; the baby must have a right to their care, or at least a right to the use of his mother's womb until birth, and this is difficult for libertarians, because this looks, on the face of it, like a positive right, which libertarians, including myself, don't believe in. In order to establish such a right, we would either have to say that the parents somehow took that obligation upon themselves voluntarily (which will be difficult to say in the case of failed birth control, and impossible to say of a woman who was raped), or that this is somehow, contrary to appearances, actually a negative right.
If we wish to take the second route, it may have profound consequences for our overall understanding of private property. For instance, we may say that if someone comes to be on your property through no fault of his own, expelling him from your property in such a way as to physically harm him constitutes an act of aggression against him, and therefore violates his (negative) rights. This will then also apply to the fetus's presence in the womb. This doesn't seem like a bad position for a libertarian to take overall, but I'm having trouble seeing clearly what, if any, are the ramifications for the case of, for instance, forcibly expelling a burglar from one's house. In this case, you are defending against an act of agression, and this makes our exercise of force acceptable. If the person didn't know he was trespassing, or something, he wouldn't be agressive, and therefore we couldn't expel him by force in such a way as to harm him. Sounds good to me. Interestingly, the Talmud (don't ask me for the exact citation, but I know I read this in Jewish Law class freshman year) says that when the mother's life is endangered, the fetus becomes an agressor, and describes in graphic terms cutting the fetus to pieces in the birth canal in order to save the mother's life, saying that this is not only permissible, but obligatory, but nevertheless prohibits abortion in the general case.
At any rate, my general point is this: if the parents have an obligation to the fetus to care for it, abortion will be immoral, but only if the fetus has a right to the care of the parents will the illegalization of abortion be legitimate. I do, in fact, think that the fetus has such a right, in addition to the parents' obligation, but I think that the right is much more difficult to establish than the obligation.