The Best Comparison between Abortion and Slavery I've Seen

Third Wave Agenda, a pro-choice blog, has asked the following excellent questions:

4. Do you think it is possible to have a society where there is no abortion, but there is sex? Consider that abortion has been documented in nearly every society, at every time; that abortion techniques are cited in the oldest known medical texts; that abortion began being considered "sinful" after a whole mix of political issues; that many societies throughout history placed no stigma on abortion; that both Plato and Aristotle have written about abortion as a necessary aspect of a functioning society; that St. Augustine believed abortion only required penance for the sexual aspect of the sin ("There cannot yet be said to be a live soul in a body that lacks sensation"); and that I know of no society where abortion does not exist or has never exited. So is there such a place? Is it possible to have a society without abortion? Where has there been such a place? The only answer I've gotten to this question is "Eden before the fall." That's all good and fine, and while I happen to believe that such a place existed, there isn't much of a historical record on it. Know of any others? Is it even possible?

A similar series of questions could have been asked about slavery at the time the anti-slavery movement was getting started.