One very popular liberal line of argument involves arguing that there is another right involved, besides any right to life that the embryo or fetus may have - namely, the woman's right to control what happens inside her own body. The situation, accordingly, is one where there is a conflict of rights, and so one can attempt to argue that abortion is not wrong all things considered, because the woman's right to control what happens insider her own body counterbalances any right to life that the embryo or fetus may have.
The difficulty that this argument faces is that it is far from clear that the right to determine what happens inside of one's own body is at least as serious a right as the right to life. Imagine, for example, that there is a small transmitter inside of one's body that one is not aware of, that is not a threat to one's future health, that cannot be removed without being destroyed, and whose existence is necessary to maintain the life of someone outside of one's body. (Perhaps it transmits signals to a pacemaker inside that person.) Is it clear that it is morally permissible for one to remove that transmitter from one's body?
