One of the best papers arguing for the pro-choice position I have ever read was “A Defense of Abortion” by Judith Jarvis Thompson, which was used to represent the pro-choice argument on the abortion question in my introductory ethics class. It comes close to the position that catsix seems to hold, and having read through many of the posts in this thread, I thought I would bring some of Thompson’s main points to the table.
She argues first of all in defense of abortion due to rape by using this analogy: suppose you woke up one morning in a hospital bed, with tubes attached to your kidneys and running to a machine that filters your blood into a person’s body lying next to you, who happens to be a famous violinist. Someone informs you that he suffers from a serious illness and requires this filtration to survive, and only your blood is compatible. Assuming you had been placed in this position against your will, and that in order to complete the procedure you would be required to lie there and allow your blood to be shared with his system for nine months, would you be ethically required to do so?
Obviously, you wouldn’t, and it’s pretty clear how this would apply to a pregnancy situation caused by rape—it’s not the embryo’s/fetus’s fault it’s there, any more than it was the violinist’s fault he was there, but in neither situation have you given either one a right to your body, and therefore you would have a right to separate yourself from them, even if they were to die.
But that argument only works clearly for abortion due to rape, which most people don’t object to anyway (at least, not to the point that they believe it should be legally forbidden). What about in a case where you knowingly had sex, but don’t want children? In a case where a contraceptive failed or a condom broke, it seems to me like it’s not that far removed from a rape case—there may not be a person forcing herself or himself on you, but you’ve still done everything in your power to protect yourself while engaging in something that you have a legal right to do. Thus, the resulting embryo/fetus would not, it seems to me, have a legal right to your body.
Essentially, I believe that abortion should be, at least legally, permissible in any situation in which the mother did not give the fetus a right to her body (in other words, in any situation in which she did not want it). It follows as a practical consideration that abortion cannot feasibly be prohibited at all, then, because there’s no way to know—outside of asking a mother directly—whether or not she ever, in effect, gave a fetus permission to use her body.
Ethically, the point of contention for me is whether or not it would be immoral for a woman to abort a child she conceived through consensual, unprotected sex. As I see it, what makes this morally different from a case in which preventative measures failed is that both men and women know that there is a significant likelihood that pregnancy will result from unprotected sex, and thus doing so with knowledge of the risks is equivalent to accepting the risks. I’m not aware of an argument that conclusively defends this, and while I would not condone legal prohibition of abortion under these circumstances, it seems like abortion would be morally wrong (and irresponsible) in this case.