If we consider abortion as something that prevents the rise of future human beings, why can't we say the same for abstinence or the use of birth control?  Instead on thinking about how many possible prodigies have been denied life beause of abortion, think of how many have prevented simply by a pair using protection, or not sopulating to begin with.  If someone recieves an abortion, their story ends in the same way that it would have if they had used birth control methods or participated in abstinence on the night of conception.  In a way, an abortion is just hindsight's version of birth control.