During the 2012 election cycle, the Democratic Party enjoyed considerable success staking out strongly liberal positions on gay marriage and contraception. Now, apparently, leading Democrats and powerful liberal interest groups are pondering whether to extend this muscular social-issues agenda to the abortion-rights cause — in some cases, by working to guarantee the availability of late-term abortions. The temptation to lump all social issues together is understandable after liberals' 2012 success. But giving in to it would be politically foolish and morally reckless.

To begin to see why, consider what has enabled Democrats to exploit contraception and gay marriage for political gain.

Nearly all American women (99 percent) have used birth control at least once, more than 60 percent of women currently use it, and a strong majority (63 percent) of all Americans support forcing employee-provided health insurance plans to cover contraception. For the huge numbers of voters in these camps, birth control and the ObamaCare contraception mandate are moral non-issues — and so the Democrats have nothing to lose and quite a lot to gain by portraying themselves as absolute champions of birth control.

The GOP, by contrast, is divided on the topic. Most of those who oppose the contraception mandate are Republicans, and it makes sense to assume that the bulk of the 15 percent of Catholics who follow the Vatican's lead in condemning the use of artificial forms of contraception lean toward the GOP as well. That makes birth control electorally problematic for Republicans in a way this it just isn't for Democrats.

A similar dynamic can be seen with gay marriage. While the issue remains considerably more contentious than contraception — with many Americans, especially traditionalist religious believers of many faiths, opposing it for theological and moral reasons — the tide of public opinion is shifting in gay marriage's favor with astonishing speed.

With roughly 50 percent of Americans now supporting gay marriage (and the rate far higher among those 18-34 years of age), the Democrats (from the president on down) have decided that they now have more to gain by offering robust support for gay rights than by opposing it. And they're probably right.

But from the standpoint of public opinion as well as moral reasoning, abortion belongs in a different category. A recent Pew poll nicely captures America's deeply conflicted views on the issue, with strong support for upholding Roe v. Wade (63 percent) combined with nearly half the country (47 percent) saying that abortion is morally wrong and only 13 percent describing it as morally acceptable. 

Abortion is among the most thoroughly tragic issues in our public life. This is not a moral condemnation; it is a moral observation. A tragedy in the classical sense is a situation that pits two legitimate moral claims against each other in such a way that one or the other must be sacrificed, despite its legitimacy. That describes the dilemma of abortion exactly: A woman who learns of an unwanted pregnancy finds that her own good and the good of the fetus lie on a collision course. The woman's moral status is clear, or should be clear, to everyone.

The fetus' moral status, by contrast, is murkier. Some — orthodox Catholics and many other traditionalist religious believers — consider that status obvious. But many others do not — and their views are based on widely shared moral intuitions and cultural practices. Couples do not normally grieve for a miscarried fetus with anything like the intensity that they do for a child who dies after birth. Neither will most couples choose to bury a fetus that has failed to make it to term. It is likewise a firmly established custom to measure human age from the time of birth, not from the time of conception. In these and innumerable other ways, we testify to the significance of birth as a threshold separating distinct phases of life. At birth, we become full-fledged residents of the human world that is governed by morality and law; but prior to birth, we exist in a kind of antechamber to that world, not quite the rights-bearing individuals we will be once we fully commence our lives outside the womb. 

And yet, progress in science and technology has been slowly strengthening the case for the humanity — and moral status — of the fetus. Unlike the 13th-century Thomas Aquinas, who believed the soul entered the fetus at "quickening" (the point, usually during the second trimester, when the pregnant woman feels the first stirrings of the fetus inside her), we now know that the fertilized egg becomes an embryo at some point between 10 and 14 days after conception — and that the embryo is genetically a distinct person, albeit an immature one. The old debate about whether "life begins at conception" is now beside the point. The science of embryology clearly shows that personal identity begins roughly two weeks after conception — something brought home to most parents several weeks later when they get to see actual images of their baby in increasingly sophisticated ultrasound scans. To terminate a pregnancy after two weeks terminates the life of a person at a very early stage of development. We can argue about the moral status of this person, but not about its status as a person.

Given the ambiguity in the moral status of the fetus and the fact that it resides within the body of a human being with inviolable rights, it makes sense that public opinion about abortion is so untidy, with strong support for a first trimester right to choose, but less and less support for that right later in pregnancy, the closer the fetus comes to viability. Many people unwilling to describe as murder the termination of a microscopic clump of cells become quite confident in doing so when contemplating an abortion during the third trimester. That moral judgment is neither deluded nor misogynistic.

Such judgments also shift in response to the motive for seeking out an abortion. When the life of the mother is at stake — perhaps the most tragic trade-off of all — there is great sympathy and support for the pregnant woman's choice. On the other hand, many Americans are deeply troubled by the thought of women using their reproductive freedom to procure abortions — especially serial abortions — for frivolous reasons. What counts as frivolous? Above all, the use of abortion as an after-the-fact form of birth control.

And this judgment, too, makes sense. Before the sexual revolution of the 1960s and '70s, contraception was often hard to come by, while a pregnancy out of wedlock would in most cases lead a woman to be socially stigmatized. That is not true today. Women have more ways than ever to prevent unwanted pregnancies, as well as a greater range of socially acceptable options for dealing with one when it happens. And that means, oddly enough, that the sexual liberation of the past few decades has helped to create an environment in which there are now fewer situations in which choosing to have an abortion seems morally justifiable. 

All of these moral considerations contribute to America's conflicted views on abortion. As long as these views remain conflicted, staking out extreme positions will be politically unwise. That certainly holds for anti-abortion absolutists on the Right (especially when they begin speculating about "legitimate rape" and whether some pregnancies following sexual assault are "something God intended to happen"). But it also applies to liberals eager to become champions of an equally absolute right to choose. 

Damon Linker is a senior writing fellow at the University of Pennsylvania, a contributing editor at The New Republic, and the author of The Theocons and The Religious Test. You can follow him on Twitter: @DamonLinker.