Thus, according to Roe and Casey, only after viability may the state, in theory if not really in practice (given the mandatory post-viability exception defined broadly in Doe v. Bolton), choose to protect the unborn. Before viability, the Court decided, the killing of human beings in utero must be permitted for any reason.
But what constitutional, legal, historical, or moral justification is there for supposing that the physical dependence of one human being on another requires that the law permit the killing of the former?
Here is the Court's entire argument in Roe v. Wade for using the viability criterion:
With respect to the State's important and legitimate interest in potential life, the "compelling" point is at viability. This is so because the fetus then presumably has the capability of meaningful life outside the mother's womb.
That's seriously the entire argument (you can read the Roe decision for yourself). It is, of course, circular reasoning. Viability is important, the Court says, because that's when a child can live outside the womb (the definition of viability). Viability is important, that is, because it is viability.
"[T]he Court's defense seems to mistake a definition for a syllogism," noted the eminent Yale law professor John Hart Ely (who personally supported legalized abortion). Indeed, "scholars from a wide variety of backgrounds have recognized," writes University of Georgia law professor Randy Beck, that "Roe literally provided no argument in favor of treating viability as the controlling line, much less an argument grounded in constitutional principles."
Did the Court at least manage to offer a reason for the viability criterion when it reconsidered the issue in Planned Parenthood v. Casey? Amazingly, no. Here is the Court's argument in Casey:
[V]iability, as we noted in Roe, is the time at which there is a realistic possibility of maintaining and nourishing a life outside the womb, so that the independent existence of the second life can, in reason and all fairness, be the object of state protection that now overrides the rights of the woman.
This, again, is not actually an argument. The Court simply provides the definition of viability and then, without offering any reason, concludes that it makes all the difference in deciding who may be protected from lethal violence and who may not be. If we do take this to be an "argument," it is a fallacious one, as Francis J. Beckwith writes:
For the Court to make its argument valid, it would have to add to its factual premise [the fact of fetal non-viability] the normative premise: whenever a human being cannot live on its own because it uniquely depends on another human being for its physical existence, it is permissible for the second human being to kill the first to rid the second of the burden.
The Court assumed that premise in both Roe and Casey. The Court has never argued for it.
The private papers of the justices suggest that the author of Roe, Justice Harry Blackmun, under the influence of Justice Lewis Powell and others, chose viability arbitrarily after considering other, equally arbitrary criteria. Justices Powell and Thurgood Marshall favored drawing the line at viability (rather than earlier) for the practical reason that it allowed a larger window of time during which women could have abortions—a policy outcome that the justices personally liked.
A decade later, Justice Sandra Day O'Connor (in her dissent in Akron v. Akron Center for Reproductive Health), who went on to co-author the plurality opinion in Casey, called viability "no less arbitrary" than any other point in pregnancy. And the Casey decision itself acknowledged that viability "may seem somewhat arbitrary," but held that, nevertheless, the right to abortion "must not be extinguished for want of a line that is clear."
So the justices (in both Roe and Casey) had, as far as we know, no reason whatsoever for thinking that viability is of actual significance (constitutionally or morally). That explains why they have never been able to give any reason.
"The arbitrariness of the viability line is confirmed," wrote dissenting Justice Antonin Scalia in a footnote to his Casey opinion, "by the Court's inability to offer any justification for it beyond the conclusory assertion that it is only at that point that the unborn child's life 'can in reason and all fairness' be thought to override the interests of the mother." Scalia added:
Precisely why is it that, at the magical second when machines currently in use (though not necessarily available to the particular woman) are able to keep an unborn child alive apart from its mother, the creature is suddenly able (under our Constitution) to be protected by law, whereas, before that magical second, it was not? That makes no more sense than according infants legal protection only after the point when they can feed themselves.
In its Casey decision, the Court wrote, "[A] decision without principled justification would be no judicial act at all." That's true. Roe v. Wade and Planned Parenthood v. Casey, therefore, are not judicial acts. They are judicial embarrassments.