Different people will have different views about this, but I think the obvious thing to say is this. Taking the potion you described harms a person who will one day exist. Having an abortion does not harm a person who will one day exist. So that is the difference: In the one case, a person is harmed, but not in the other. That person does not exist at the time the harm is done, but I think you are correct that the person does not need to exist at that time to be harmed.

To see the importance of this, note that a similar case can be described even if the woman takes the potion before any child is conceived. In that case, no independent life exists at all, and yet it seems as if taking the potion is morally objectionable, for much the same reason.

There are complications here, surrounding the idea that the woman's behavior is wrong even if no child is ever conceived, on the ground that she risked harming someone. But I'll leave it to you, and others, to work this out. One important point is that, so far as I can see, "X risked harming someone" does not imply "There is someone X risked harming", any more than "X was baking a cake when she died" implies "There was a cake that X was baking when she died." (X died before any such cake came into existence.)

Let's agree that, from the moment of conception, we have a living thing -- and, if the parents are human, this living thing belongs to no other species than homo sapiens. So what? That fact doesn't in itself determine the moral status of the product of conception.

Here's one possible view: as the human zygote/embryo/foetus develops, its death becomes a more serious matter. At the very beginning, its death is of little consequence; as time goes on its death is a matter it becomes appropriate to be more concerned about.

In fact, that view seems to be exactly the one most of us take about the natural death of human zygotes/embryos/foetuses. After all, few of us are worried by the fact that a high proportion of conceptions spontaneously abort: few of us are scandalized if a woman who finds she is pregnant by mistake in a test one week after conception is pleased when she discovers that the pregnancy has naturally terminated a few days later. Similarly for accidental death: suppose a woman finds she is a week pregnant, goes cross-country horse riding, falls badly at a jump, and spontaneously aborts. That might be regrettable, but we wouldn't think she'd done something terrible by going riding and running the risk. (Compare: we do think it is a matter for moral concern that there are high levels of infant mortality in some countries; we would be scandalized by a woman celebrating the death of an unwanted newborn baby: we would be appalled at someone risking the life of nearly nine-months old foetus by going in for some potentially dangerous sports.)

So: our attitudes to the natural or accidental death of the products of conception seem to suggest that we regard them as of relatively lowly moral status at the beginning of their lives, and of greater moral standing as time passes. It would be consistent with such a view to take a similar line about unnatural deaths. For example, it would be consistent with that to think that using the morning-after pill is of no moral significance, while bringing about the death of an eight month foetus is getting on for as serious as killing a neonate, with a gradual increase in the seriousness of the killing in between.

Now, the point I'm making here isn't that this "gradualist" view is right (actually, I think it is, but you don't have to agree for present purposes). The point is that it that it isn't obvious that it is wrong. In other words, it isn't obvious that an all-or-nothing attitude to members of the species homo sapiens has to be right. It is not obvious that agreeing that the products of human conceptions are also human means that we should assign them all the moral weight we give to developed human beings. There's room for argument.

The idea of giving rights to fetuses as soon as they are capable of consciousness is, I think, discussed in the literature. Fetuses have a functioning central nervous system very early in pregnancy (typically before pregnancy is detected) and possibly consciousness of some sort starts at this point. Probably you should also be willing to extend your ideas about the importance of consciousness to human rights later in life (e.g. to comatose patients).

Some writers on abortion argue that fetuses have rights to life before the onset of consciousness, and perhaps you might be interested at looking at these e.g. Don Marquis.

I wonder what you mean when you say that "many people attempt to devalue the controversy "?

I suppose that it is true that a lot of people are not at all tempted by either "end of the field" -- if that means holding at one end that abortion is tantamount to murder, or holding at the other end that even very late abortions are morally insignificant. Many people think that the moral status of an zygote/embryo/foetus increases as time goes by -- the natural or unnatural death of the immediate product of conception is of little or no consequence, the natural or unnatural death of a foetus near term a matter of very serious concern, with a sliding scale in between. If you take this "gradualist" view -- a rather attractive one, I think -- the loud controversy between extremists at either end will indeed seem wrongheaded: it's not that the gradualist ignores the controversy, or merely ducks out from taking sides, rather she thinks that there is a third option.

I've written a bit more about that kind of gradualism in answer to an earlier question here.

If someone says of a (human) foetus that it is not human, then presumably they are not making a biological remark. They are not foolishly assigning it to the wrong species!

Rather, they are expressing -- not in a very happy way -- a moral view. The claim is that a foetus. at least at sufficiently early stages in its development, doesn't have the same moral status as a developed human being (a fully-fledged person).

Now, given the gradual biological development, it would -- as the question implies -- seem intolerable to suppose that there is, somewhere along the line between conception and birth and beyond, a point where there is a sudden jump from having no moral standing to having the standing of a full person. The natural view is that there is a corresponding increase in moral standing as you go along. And indeed, that seems to be what almost everyone actually thinks when considering the natural death of embryos and foetuses. A high percentage of conceptions (over 25%) result in very early natural terminations: we don't, in practice, think of that as a moral scandal as we might regard a similar level of neo-natal death. We don't think of a woman's rejoicing when an unwanted pregnancy naturally comes to an end after a couple of weeks as being on a par with a woman celebrating the death of an unwanted baby. The fundamental "pro-choice" thought is that we should think of the seriousness of bringing about the death of embryos and foetuses in proportion to the seriousness with which we do in fact mostly regard natural deaths of such things -- i.e. not very serious (so not on a par with the killing of a developed person) at the very outset, more serious as time progresses. But putting that thought in slogan form, and saying that foetuses aren't human, would -- I agree -- be misleading, to say the least.

And for yet another persepctive on this, it seems as if it is morally permissible not always to be a "good samaritan". But of course one might reasonably regret not having been a "good samaritan" on some particular occasion, i.e., regret not having gone out of one's way---beyond the call of moral duty---to do something for someone. It therefore seems perfectly reasonable, in general, to regret things one had, and knows one had, every moral permission to do.

A cognate point is made explicitly in Judith Jarvis Thomson's classic paper, "A Defense of Abortion". To say that something is morally permissible is simply to say that it isn't morally prohibited: It's a fairly weak claim in some ways. In particular, it doesn't at all follow that the thing in question is, all things considered, the best thing to do, nor even that it is, all things considered, a particularly nice thing to do. So, if I remember correctly, Thomson says she is quite willing to concede, so far as her argument is concerned, that it might always be the nice thing to do not to have an abortion. That, however, is not what is at issue.

That morality leaves a good deal open is so intuitive that utilitarianism's failure to leave a good deal open, in this sense, is often considered one of the more serious objections to it.

That set of attitudes wouldn't be irrational at all for a woman who discovers herself infertile or wanting to have had more children some time after the abortion. Even if a fetus is not a person, and it's entirely permissible to have an abortion, it's obviously true that fetuses eventually turn into persons. So an entirely permissible abortion can later on seem to have been a mistake.

There's no obvious inconsistency. The fact that something is morally permissible doesn't mean that there's never any reason to regret having done it. To take a very different sort of example: suppose I'm very busy, and I pass up an opportunity to go on a trip to some intriguing place, deciding instead to stick to my work. I might end up regretting my decision, even though it wasn't wrong of me to decide as I did. I might come to think I missed out on a valuable opportunity and that it would have been worth rearranging my work for the sake of it.

Perhaps this doesn't quite get at your worry. Perhaps what you have in mind is someone who thinks that abortion is morally permissible, but who come to have moral regrets about having had one. That sounds more like some sort of inconsistency, but it needn't be. If the thought is "It was morally permissible for me to do this, but it was wrong of me to do it," then perhaps we have an inconsistency. But it's possible to think that something is permissible in general, and yet to think that given one's own situation, the morally better thing for oneself would have been to decide differently. In other words, questions about what's permissible in general may not be fine-grained enough to decide what's best in one's own particular moral circumstances.

There is more relevant discussion in response to Question 2107, where I remark on the moral differences between early fetuses and newborn infants that we seem to make in our thinking about the natural or accidental death of fetuses as against babies.

In addition to Allen's points, it should be noted that not everyone agrees that the issue of abortion boils down to the issue of whether the fetus is a person. Judith Thomson has famously argued that other persons do not have a right to use my body, even if preventing them from such use would cause their death. For example, if I had a rare blood type and was taken into custody an hooked up to someone who needed blood of my type, this would be a violation of my rights and I would be permitted to resist, or unplug myself. Because a fetus is using the pregnant woman's body, sometimes against her will (think of rape especially, but also contraception failure), she does not have a moral obligation to allow such use. In some cases it would be very kind of me to allow such use, e.g., if it wasn't at great cost to me, but even if we count the fetus as a ful person, it doesn't have a right to such use.

See: Judith Jarvis Thomson: A Defense of Abortion. Philosophy & Public Affairs, Vol. 1, no. 1 (Fall 1971).