Most discussion of the issue bogs down in minutiae about when human life begins, when or if the fetus can be considered to be alive, etc. All this is really irrelevant to the issue of the legality (again, not necessarily the morality) of abortion. The Catholic antiabortionist, for example, declares that all that he wants for the fetus is the rights of any human being—i.e., the right not to be murdered. But there is more involved here, and this is the crucial consideration. If we are to treat the fetus as having the same rights as humans, then let us ask: What human has the right to remain, unbidden, as an unwanted parasite within some other human being’s body? This is the nub of the issue: the absolute right of every person and hence every woman, to the ownership of her own body. What the mother is doing in an abortion is causing an unwanted entity within her body to be ejected from it: If the fetus dies, this does not rebut the point that no being has a right to live, unbidden, as a parasite within or upon some person’s body.
The common retort that the mother either originally wanted or at least was responsible for placing the fetus within her body is, again, beside the point. Even in the stronger case where the mother originally wanted the child, the mother, as the property owner in her own body, has the right to change her mind and to eject it.
For a New Liberty, p.139