Millions of women obtain abortions because they do not want baby girls.

It’s shocking, but incontrovertible. Two decades ago, Harvard economist Amartya Sen, in an arrestingly titled article, documented the statistical reality that “More Than 100 Million Women Are Missing.” In a recently published book, Unnatural Selection, journalist Mara Hvistendahl convincingly demonstrates that the overwhelming reason for the increasingly large demographic disparity in the male-female birth ratio is sex-selection abortion. Hvistendahl estimates the number of missing or dead now to be 160 million and counting. Women have abortions because (among other reasons) they are able to learn the sex of their unborn baby and kill her if she’s a girl.

The phenomenon is most pronounced in certain Asian populations where the birth of girls is especially discouraged, but is not limited to Asia. Hvistendahl shows that sex-selection is not culturally or uniquely Asian. Male-child preference exists everywhere. Sex-selection abortion rises as birth rates fall, as wealth increases (especially in developing nations), and as technology for identifying a child’s gender in utero becomes more reliable and more available.

Sex-selection abortion occurs in America, too, and the practice is likely to increase. In August, a study in the Journal of the American Medical Association reported that a simple blood test seven weeks into pregnancy can reliably identify the sex of the child. Watch for a spike in abortion rates over the next few years as parents find it easier and cheaper to “choose” to have a boy by killing the fetus if—in a bitter reversal of an expression of joy—“it’s a girl.”

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The shocking reality of sex-selection abortion cries out for laws banning the practice. Polls have shown that about 95 percent of the American people oppose sex-selection abortion. Even those who style themselves “pro-choice” overwhelmingly agree that abortion should not be allowed when the reason for such a choice is that the child to be born is female. The most pernicious radical feminist argument for abortion rights—that abortion is essential for “gender equality”—doubles back on itself in the case of sex-selection abortion: if abortion on the basis of the sex of the child—killing girls because they are not boys—is not sex discrimination, it is hard to know what is. (Hvistendahl is, awkwardly, pro-choice, yet horrified by the consequences of “unnatural selection.”)

Four states—Illinois, Pennsylvania, Oklahoma, and most recently Arizona—have enacted laws prohibiting sex-selection abortion. Those laws have yet to be tested in the courts. At least seven other states have considered bills that would ban the practice. A sex-selection-ban bill was introduced in Congress in 2009—I worked with committee staff on the bill—but it died in the then Democrat-controlled House.

Are such bans constitutional under the Supreme Court’s decisions creating a right to abortion? The question such laws present is a dramatic one, challenging the underpinnings of Roe v. Wade in the most fundamental and direct of ways: Does the U.S. Constitution create a right to abortion, even when the woman’s reason for abortion is that she does not like the sex of her unborn child?

Sadly, the answer, under the Supreme Court’s absurd, through-the-looking-glass constitutional law of abortion, is yes. Under Roe and the Court’s 1992 decision in Planned Parenthood v. Casey, a woman has a constitutional right to abort for any reason up to the point of “viability,” when the child could live outside the mother’s womb. Even after viability, a woman may abort for any “health” reason, an exception that ends up swallowing the rule: the Court’s abortion decisions define “health” justifications for abortion to include any “emotional,” “psychological,” or “familial” reason for wanting an abortion.

A pregnant woman’s (or a couple’s) preference for a boy rather than a girl would seem to fit comfortably within the gaping loophole for “emotional” or “familial” reasons for abortion. Parents are thus free to choose to kill female human fetuses because they are female, even when the unborn child could live outside her mother’s womb. It thus appears that, under Roe and Casey, laws banning sex-selection abortions are unconstitutional through all nine months of pregnancy.

This, of course, is madness, and it highlights, in an especially persuasive way, the extreme madness of the Supreme Court’s current abortion doctrine. It exposes the grim legal reality that abortions may be had for any reason. It lays bare the doublespeak of “health” justifications for abortions, and it highlights the logical (and moral) incoherence of abortion-rights arguments predicated on notions of “women’s rights” or “equal protection”: a right to abortion, in the name of gender equality, ends up being a right to abort females.

The fact that laws banning sex-selection may fly in the face of the Roe and Casey decisions is no reason not to enact them. On the contrary, it is a powerful reason to enact them: the justices, and abortion supporters generally, ought to be forced to confront the uncomfortable reality of the Court’s abortion jurisprudence. Those who style themselves as “centrists” or “moderates” on abortion–such as those who claim to be “personally opposed but pro-choice” or who acquiesce to Roe’s abortion regime for some other political or social reason—need to understand precisely what such a position entails and the lethal logic of what they have agreed to accept.

This goes for Supreme Court justices, as well. Justice Anthony Kennedy, whose vote was pivotal to the 1992 Casey decision reaffirming Roe on grounds of stare decisis, professed himself shocked— shocked!—to discover a few years later that the logic of Casey yielded a constitutional right to partial-birth abortion. He had not realized that a plenary right to “choice” on abortion meant that a physician could induce labor, deliver an intact, living baby except for the head, puncture the child’s skull, vacuum out its contents, and then complete delivery. Kennedy found himself outvoted, 5–4, and thus dissented in the 2000 Stenberg v. Carhart decision, recognizing a constitutional right to partial-birth abortion. He wrote the majority opinion narrowly upholding the federal partial-birth abortion ban, 5–4, in Gonzales v. Carhart in 2007. (Alas, Kennedy reaffirmed the “health” exception and the Court only distinguished, and did not overrule, its earlier partial-birth ruling. In the end, Gonzales holds only that partial-birth abortion can be banned only if it is clear that an equally “safe” abortion is available by some other method.)

Being confronted with a harsh reality can change the minds of persons who have thought about a question only in abstract, arid terms. It is possible, then, that even a pro-abortion Court, confronted with a law banning sex-selection abortion, might recognize and retreat from the consequences of its own prior decisions. Enacting sex-selection bans, even if contrary to Roe and Casey, just might lead the Court to begin charting a path away from Roe.

A sex-selection ban would indeed present the Supreme Court with a dilemma. To strike down such a law—in essence, to embrace a constitutional right to sex-selection abortion—would expose just how extreme and immoral the Court’s present abortion doctrine really is. To read such a result in the name of “gender equality” would be monstrous and absurd. Such a ruling would undermine support both for Roe and for the Court as an institution as never before. (Concern for the Court’s own prestige and public support was, in fact, part of the reasoning in Casey for reaffirming Roe.) A sex-selection ban dares the pro-abortion justices to embrace an abortion right to kill girls for being girls. Such a ruling would expose the illegitimacy of the Court’s abortion decisions.

On the other hand, for the Court to uphold a ban on such abortions would require a concession with powerful symbolic consequences: the human fetus has a gender; and killing a living fetus on the basis of such a distinctive, personal, permanent feature of human identity is unthinkable, and may rightly be punished. Such a concession would undermine the moral and legal premises of the entire judicially created right to abortion. If abortion merely removes unwanted tissue, its gender does not matter. But if gender matters, it must be because the unborn living being in the womb is already a human child, not merely “potential” life. The issue of sex-selection abortion thus challenges the very “it”-ness of the living human embryo or fetus killed by abortion—the implicit non-humanity of the fetus that underlies most arguments for allowing abortion. It is a girl or a boy—a member of the human family, albeit an extremely vulnerable one, whose life hangs in the balance. Acknowledge the humanity of the fetus and the regime of Roe collapses.

It is unclear which horn of the dilemma the Court would choose today. Four justices (Roberts, Scalia, Thomas, and Alito) would almost certainly uphold a sex-selection ban. Indeed, they would probably all agree that Roe and Casey were wrongly decided, and could properly be overruled. Four justices (Ginsburg, Breyer, Sotomayor, and Kagan) would probably hold that Roe’s right of choice is inviolable and, yes, that abortion is allowable for any reason a woman chooses. Justice Ruth Bader Ginsburg has explicitly defended Roe’s result on “feminist” grounds of sex equality. It would be interesting, and revealing, to see if she would affirm an absolute constitutional right to abort female human fetuses because they are female, in the face of a state or a federal ban forbidding sex-discrimination abortions. Would the woman who built her fame as a crusader against gender discrimination end up embracing fetal gendercide?

That leaves Justice Kennedy, whose votes in abortion cases have reflected a wet-finger-to-the-wind approach driven by the desire to appear moderate, by extreme sensitivity to elite public opinion, and by a concern to preserve the Court’s political capital and prestige. He has voted, alternately, to replace Roe (in 1989), to reaffirm Roe on the basis of stare decisis (in 1992), to deny a right to partial-birth abortion (in 2000) and, most recently, to accept but cut back on such a right (in 2007). His vote, more than that of any other justice, will be susceptible to the political winds and attuned to a decision’s effect on public perceptions of the Court as an institution and of him personally. He might provide a fifth vote to uphold a ban on sex-selection abortion, but would be unlikely to support any full-scale reversal of Roe’s or Casey’s core premises.

The intellectual, constitutional, legal case against the legitimacy of Roe already has been won. Roe hangs on by the thread of stare decisis, which in turn is a function of a few justices’ perception of the need to adhere to a concededly indefensible precedent for essentially social and policy reasons rooted in believed public support for the outcome. Knock out the prop of public support, and Roe falls.

In making this specific issue, sex-selection abortion, the pressure point of political and legal debate, and of public discourse over the constitutional status of abortion rights, we can frame the discussion in terms most favorable to the pro-life stance, most persuasive to those who are undecided or uncommitted, and most uncomfortable for defenders of the extreme pro-abortion status quo. The result of any test case, down the road, very likely turns on whether President Obama has a chance to make further appointments to the Court.

This suggests yet another reason for pressing this issue in the form of a proposed federal law banning sex-selection abortion. Not just pro-choice justices, but also pro-choice politicians need to be confronted with, and called to account for, the lethal logic and terrible consequences of their support of Roe. President Obama, and pro-choice members of Congress and state legislatures, should be put to a straightforward test: Do you support or oppose a right to abortion for reasons of sex-selection? Should a woman have a constitutional right to abortion because “it’s a girl”? There is no better litmus test issue over life, and there is no better time for pressing such a challenge than during an election year.