I will argue for this by presenting an analogy presented by Thomson in her paper. In this analogy, Thomson presents a situation: You have been kidnapped by a music group to have your kidneys hooked up to a famous ailing violinists body for nine months in order for him to survive. Thomson claims that it would not be unjust or morally impermissible for you to unplug yourself from the violinists body because he has been granted no right to use your body (Thomson p. 30). Now, I will use this analogy to argue for when it would be unjust to unplug yourself from the violinists body. Suppose, for example, that this music group had asked you for permission to use your body prior to plugging you into the violinist. Say, that you gave them permission and agreed to be attached to the violinist for nine months. However, later on, you decide that you have better things to do than to be stuck to this violinist for nine months, and then decide to unplug yourself from the violinist, leading to his death. That act would be an unjust killing; because you gave the violinist the right to use your body, then took it away from him.
I will now use the example of an actual pregnancy to defend my argument for the unjust killing of a fetus. Suppose that a young couple, both in their mid-twenties decides to have their first child; this is your typical planned pregnancy. They buy a new home and all other certain baby necessities. However, say that during this pregnancy the couple has a change of heart. Say that spontaneously the couple decides that they do not yet desire a child. Thus, they decide to have an abortion for the child that they had previously given the right to life; they had previously given it the right to use the mothers body. It would thus be an unjust killing of the fetus, and it violates the fetus right not to be killed unjustly.
This result does not weaken Thomsons argument by any means. I say this because Thomson was arguing for when an abortion is not morally impermissible (Thomson p. 37). She was not arguing for which cases an abortion is impermissible. Therefore, further questioning as to which abortions would be unjust under Thomsons argument would be irrelevant. Also, I was able to make my argument without relinquishing any of Thomsons claims. Moreover, based on my argument, one can, in fact, make a claim for what certain cases of abortion are morally impermissible. Lastly, Thomson is merely pretending that a fetus is a person from conception in the first place, so her notion that some abortions may be unjust is irrelevant to her opponents argument (Thomson p.37)