On Jan. 22, 1973, in Roe v. Wade, the U.S. Supreme Court declared that an unborn child enjoys no constitutional protection before he or she emerges from the womb. Even after viability, the fetus in utero counts only as a "potentiality of human life." Location — in or out of the womb — thus determined whether actual human life existed and was worthy of protection under the Roe v. Wade ruling.

Let’s take a close look at Roe’s holding and at the key non-legal judgment with which the Court backs it up. Here’s an excerpt from Roe’s concluding summary:

"For the stage subsequent to viability, the State in promoting its interest in the potentiality of human life may, if it chooses, regulate and even proscribe abortion, except where it is necessary, in appropriate medical judgment, for the preservation of the life or health of the mother."

One fundamental reason that Roe v. Wade must be overturned is this: It commits our nation to a wholly irrational definition of who we are, and so of our human dignity and rights. Yet I think there are reasons to hope, most states now treat the killing of an unborn child as a kind of homicide, if committed without his or her mother’s permission. In 2004, the federal Unborn Victims of Violence Act became law. This law provides that an unborn child at every point in its development gets the same federal protection as its mother.

The first footnote in Roe v. Wade has indicated that the Court was not granting a right to abortion during the birth process itself, but in Stenberg v. Carhart the Supreme Court built on Roe to allow abortion even during the delivery of a child (i.e. abortion after a "partial birth" in which the child is pulled out feet first, right up to its neck, before his brains are suctioned out while his head still lies inside the womb).

Ironically, Carhart itself gives us a measure of confidence that reason will win out in the end. For Carhart ridicules Roe’s idea that location can matter when deciding who deserves legal protection.

"From the standpoint of the fetus, and, I should think, of any rational person, it makes no difference whether, when the skull is crushed, the fetus is entirely within the uterus or its feet are outside the uterus. … No reason of policy or morality that would allow the one would forbid the other."

Picking up on Posner’s argument, Justices Ruth Bader Ginsberg and John Paul Stevens argue that any prohibition of partial-birth abortion is (in their words) "simply irrational" because it is no more (again in their own words) "brutal," "gruesome," "cruel" and "painful" than the sort of late-pregnancy abortion already approved by Roe.

These justices concede that Roe’s original sort of abortion is at least as brutal and painful as partial-birth abortion. In arguing that it is "simply irrational" for the states to think a baby’s location can matter, they implicitly concede that Roe v. Wade itself was simply irrational in its reliance on location as a test of human existence and dignity.