"In defense of abortion" by Judith Jarvis Thomson was written in 1971. Considering abortion politics are going back in time, Thomson's philosophical essay on abortion is still relevant. She digs deeper into the issue than the public dialogue does today. What is unusual about her pro-choice argument is that it supports the right to choose while granting that life and personhood start at conception.
I started thinking about Judith Jarvis Thomson after reading the diary "The fetus is a parasite." Some commenters agreed with sasharusa's diary, others said her diary gave a bad image to the pro-choice movement as cold-hearted. "Liberalism is a mental illness" was the reaction of some pro-life blogs to her diary. My reaction was, "Damn, underneath the difficult to stomach surface and flawed definitions, this diary reminds me a lot of a philosophical essay I read as an undergrad." Thomson's essay uses the idea of parasitism to explore abortion, but Thomson concedes that a fetus is a person. Thomson avoids the flaws I see in sasharusa's diary where she ignores important distinctions.
Sasharusa prefaced "The fetus is a parasite" with "Please, remember, this is an opinion piece." I initially took that as "this is a comparison," but she seems to argue a fetus is literally a parasite. However, parasites are biologically incapable of developing into non-parasites, while fetuses are biologically designed to become self-sustaining humans. That's an important biological distinction with moral implications, and one sasharusa didn't address.
The problem with making a broad statement like calling a fetus a parasite but ignoring distinctions is it makes it easy for the other side to undermine your argument. All they have to do is simply point out the important distinctions you fail to address. Your adversaries don't have to do the hard work of engaging with your actual argument.
Thomson starts from the premise that personhood starts at conception, not because she believes that a fetus is a person, she doesn't, but because she thinks the debate is stuck:
Opponents of abortion commonly spend most of their time establishing that the fetus is a person, and hardly anytime explaining the step from there to the impermissibility of abortion. Perhaps they think the step too simple and obvious to require much comment. Or perhaps instead they are simply being economical in argument. Many of those who defend abortion rely on the premise that the fetus is not a person, but only a bit of tissue that will become a person at birth; and why pay out more arguments than you have to?
She grants personhood because she's frustrated by the automatic assumption that if a fetus is a person than abortion is impermissible. She thinks the "right to life" claim as it applies to persons living within the womb needs to be questioned.
Thomson uses a story that relates to sasharusa's claim that a fetus is a parasite. But Thomson imagines that parasite is also a human. She asks us to imagine the following:
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. The director of the hospital now tells you, "Look, we're sorry the Society of Music Lovers did this to you--we would never have permitted it if we had known. But still, they did it, and the violinist is now plugged into you. To unplug you would be to kill him. But never mind, it's only for nine months. By then he will have recovered from his ailment, and can safely be unplugged from you." Is it morally incumbent on you to accede to this situation? No doubt it would be very nice of you if you did, a great kindness. But do you have to accede to it?
It's kind of a ridiculous way to think about abortion. But it shows how there's much more to this issue than when life starts. Calling abortion murder assumes persons should be forced to undergo a life-consuming change in order to save another's life, an assumption which Thomson rightly takes issue with:
The fact that for continued life the violinist needs the continued use of your kidneys does not establish that he has a right to be given the continued use of your kidneys... a right to life does not guarantee having either a right to be given the use of or a right to be allowed continued use of another persons body
Back to sasharusa's diary. She points out the ways a fetus is like a parasite in order to show a fetus is literally a parasite. Thomson argues even if a fetus is only
like a parasite, and even if the fetus has a right to life, that does not mean the fetus's right to live is greater than the women's right over her own body. As Thomson concludes:
Indeed, with one rather striking class of exceptions [women wanting an abortion], no one in any country in the world is legally required to do anywhere near as much as this for anyone else.