Roe v. Wade is a study in unanticipated consequences. By establishing a constitutional right to abortion, the justices of the U.S. Supreme Court no doubt thought they were settling the issue for good, accelerating a process of liberalization that was already under way in 1973. But instead of consensus, the result was polarization. The issue of abortion soon after, and for the first time, took a prominent place in national political campaigns. By 1980, both major political parties had adopted extreme positions--Republicans favoring a "pro-life" constitutional amendment to ban abortion, and Democrats opposing virtually...