Thomson uses what may be termed as the people seed analogy also to explain the permissibility of unwanted pregnancies. She writes:
Imagine that people seeds grow on trees. If one is blown into your house through an open window and lands on your sofa, it will grow into a person for whom you will have to care. You want your windows open, but you don't want a person growing on your couch, so you install window screens. Unfortunately, one of these fails, and a seed ends up on your couch and grows into a person. Does this person how have the right to use your house?
Thomson contends that it is morally permissible for you to fore this person to leave since he or she does not have a right to stay in your house. She takes this case to imply that abortions are morally permissible in cases of unwanted pregnancies stemming from sex using failed contraceptives.
She objects:
Someone may argue that you are responsible for its rooting, that it does have a right to your house, because after all you could have lived out your life with bare floors and furniture, or with sealed windows and doors. But this will not do, for by the same token anyone can avoid a pregnancy due to rape by having a hysterectomy, or anyway by never leaving home without a reliable army.
