Opponents of abortion sometimes argue that a fetus "wants" to grow up into a real person. But every egg and sperm also "want" to become a person in this sense. And if that is the case, how can one defend either contraception or celibacy, both of which deny life to millions of eggs and sperms that "want" to become people, and both of which also involve repression of "natural" impulses?
The question of whether abortion is morally wrong depends on when we become "human." Unfortunately, this does not happen all at once, as in medieval fantasies of the soul's entering the body. It happens bit by bit. We must therefore make some arbitrary decision about when to confer the "right to life." Because nature offers no clear guidance about where this line should be drawn, the most humane solution is to draw it so as to minimize human suffering. I doubt, however, that opponents of abortion will accept this approach, for once you accept it, you will almost inevitably be led to precisely the same "liberal" conclusion the Supreme Court reached five years ago in Roe v. Wade.