Earlier this year, the nation celebrated—if that is the word—the 30th anniversary of the Supreme Court's 1973 decision in Roe v. Wade, which held unconstitutional most state laws regulating abortion. Since then, Roe has become a kind of icon, before which politicians genuflect so grandly that the same Senate that passed legislation banning partial-birth abortion attached a statement to the effect that the ban does not indicate any disapproval of Roe.

What we tend to forget in the continuing battle over abortion is what a truly bad constitutional decision Roe really was. I do not mean it was bad in the moral sense, although a strong case can be made that it was. I mean it was bad in the legal sense, a judicial opinion so poorly reasoned that it is remarkable Roe continues standing as probably the only unchallengeable precedent of the past 40 years.

How bad a decision was Roe? One might start with its stunning breadth. The plaintiff claimed to have been raped—this turned out not to be true, but that is a moot point—and argued that the Texas state law at issue was too burdensome, prohibiting abortions even in cases of rape. The way law has been taught for a century in the United States, courts are not supposed to reach out to decide issues not presented in the case.

Canons of judicial decision-making hold that judges should stick to the issue presented. What is immediately apparent is that in order for Jane Roe to prevail, the justices need have ruled no more than that a state lacks the power to outlaw abortion in the case of rape. A decision so framed would have left the rest of the constitutional law of abortion to be worked out case by case, an approach that almost certainly would have resulted in a more nuanced body of precedent. ...