Why don't we talk about the benefits of abortion?

A simple enough question. Why, in a society that values results, do we not discuss the benefits/costs of abortion? Abortion is a right or it is an abomination; is that all we have? What if I hate abortion, but recognize that it has helped society?

I'm referring of course to the theory of Steven Levitt, the author of Freakonomics and much-heralded young economist, who explained years ago that the disappearance of a million at-risk children who would have been born in the late 70s if not for abortion in fact was the largest reason for the significant drop in crime in the late 90s. President Clinton and the experts were talking crime epidemic, and then suddenly, piff. Crime plummeted and the problem disappeared. Why? Levitt argues abortion, and I think he may be right. But is that a kosher argument in the current political atmosphere?