In April, prosecutors in California announced that they would charge Scott Peterson with double homicide in the murder of his wife, Laci, and their eight-month-old unborn son, Conner. Mavra Stark, the president of a New Jersey chapter of the National Organization for Women, reacted with alarm: "If this is murder, well, then any time a late-term fetus is aborted, they could call it murder."
 
     The politically savvy folks at NOW headquarters quickly distanced themselves from Ms. Stark's statement, and it's easy to see why. In a national Fox News/Opinion Dynamics poll released on April 25, 84% of registered voters agreed that the double homicide charge was appropriate. What might happen to NOW's paradise of unfettered abortion if a big part of that 84% made the same inference as Ms. Stark?
 
     Congress is now considering an Unborn Victims of Violence Act; Laci Peterson's family recently asked the bill's sponsors to re-name it after Laci and Conner. Along with the Born-Alive Infants Protection Act (signed into law by President Bush last August) and a federal ban on partial-birth abortion (now working its way through Congress), the unborn-victims law embodies the incrementalist strategy pursued by pro-life groups over the past 15 years. That strategy is largely the brainchild of Amherst College Prof. Hadley Arkes.
 
     Scott Peterson is charged with double homicide, but late-term abortions are OK?
 
     In "Natural Rights and the Right to Choose" (Cambridge, 302 pages, $28), Mr. Arkes provides a bracing account of a grave moral catastrophe and his own efforts to repair it. Beginning in the late 1980s, he proposed a "modest first step": a law protecting the lives of children who survive abortions (which became the Born-Alive Act). The purpose of this bill (and later, the partial-birth abortion and unborn victims laws) was to re-establish certain premises in the law: that the unborn child has intrinsic worth and dignity -- regardless of whether it is "wanted" -- and thus deserves the law's protection.
 
     For Mr. Arkes, the right to choose an abortion has not merely resulted in the deaths of some 1.3 million unborn children each year; it is symptomatic of a larger crisis in American government. Our legal and political elites, in their effort to make abortion a constitutional right, have abandoned the natural-rights teachings of the American Founders -- in much the way defenders of slavery did in the 19th century.

     The Founders -- and Abraham Lincoln after them -- believed that through reason men could discern from nature unchanging principles of right and wrong. One of these principles is that human beings are free and equal, each possessing an intrinsic worth and dignity: No man is by nature the ruler over another man, in the way that men naturally rule over animals or GOD rules over man. Legitimate government must therefore have the consent of the governed, as the Founders expressed most clearly in the Declaration of Independence.
 
     Mr. Arkes wants to vindicate this doctrine against legal positivism, which has held sway for more than a century now. That theory claims there is no natural law, no higher standard by which we can measure the justice of man-made "positive" law. Absent this standard, Mr. Arkes notes, the very definition of human nature -- and thus, of "human rights" -- is left to the vagaries of majority opinion. That would include the "right to choose" an abortion.
 
     Though Mr. Arkes's book is something of a melange -- part legal and intellectual history, part political philosophy, part polemic, part memoir -- it succeeds brilliantly in tracing the effects of the decision to reject natural rights. He shines at exposing sloppy logic and sophistry. Many legal luminaries -- Richard Posner and Laurence Tribe among them -- fall victim to Mr. Arkes's penetrating mind. Nor does he spare such eminent conservative jurists as William Rehnquist and Robert Bork, who promote their own versions of legal positivism.
 
     Ultimately, Mr. Arkes seeks to recover an understanding of republican self-government that doesn't cede matters of moral import to a judiciary that itself rejects the idea of objective moral standards. The purpose of "modest steps" like the Born-Alive Act, he says, is to start a political conversation. He believes that the public, led by such modest steps toward a better understanding of principle, will eventually recognize the incoherence of simultaneously believing (for instance) that Conner Peterson is a murder victim and that de facto abortion on demand is morally acceptable.
 
     Indeed, what separates Conner from an aborted late-term fetus? Merely that Conner's mother "wanted" him, while the mothers of most aborted fetuses do not "want" their children. On that basis, human beings only possess the rights that others believe it is in their self-interest to accord to them. As both the Founders and Lincoln never failed to argue, down that road lies tyranny. Mr. Arkes reminds us that, whether the issue is slavery, abortion or something else, it is possible to go through the outward motions of democracy quite affably while accepting premises that destroy the moral foundation upon which self-government stands.
 
     Mr. Bockhorn is associate editor at The Weekly Standard.