Abortion is a great tragedy, but it is also a powerful spotlight that illuminates American inconsistencies about when the use of government force is justified.

The country has just endured an angry debate over whether businesses whose owners object to gay marriages on religious grounds should be forced to assist them anyway. Generally speaking, liberals said: Yes, because the principle of equal treatment trumps freedom of conscience. Generally speaking, conservatives and libertarians said the opposite. (If you want to read a calm, intelligent and thought-provoking piece on the subject, check out "Discriminating Between Discriminations" at juliansanchez.com.)

As with any complex debate, however, this one involved more than just two ways of parsing the issue.

GOP presidential hopeful Marco Rubio recently drew a distinction between discriminating against people (e.g., by refusing to serve an LGBT customer at a restaurant) and declining to participate in an event (e.g., by refusing to officiate at a same-sex wedding). And there is another distinction, spelled out in an amicus brief by Eugene Volokh in the Elane Photography case, between forcing people to provide services that have no expressive component (such as driving a limousine) and services that do (such as writing press releases for various groups).

Given that, as Volokh wrote, "speech compulsions are generally as unconstitutional as speech restrictions," you could argue that photographers, writers, and perhaps even cake-makers have a First Amendment right not to provide expressive content with which they disagree.

Consider, for instance, whether a Jewish printer should have to print placards promoting the American Nazi Party. Or consider the views of Kathy Trautvetter, a lesbian who owns a T-shirt company. Despite her sexual orientation, she defended a Christian printer's right not to make signs for a gay-pride event: "When I read the story I immediately felt, 'If I were in his shoes, what would they be forcing me to do?'?"

But the Supreme Court did not hear the Elane Photography case, which groups such as the ACLU took as a victory over the free-speech argument: "A commercial business cannot solicit customers from the general public to buy its services as a photographer for hire and then claim that taking those photographs is a form of its own autonomous expressive activity."

Yet this doesn't mean the question of compelled speech is moot. In December the U.S. Court of Appeals for the 4th Circuit in Richmond struck down a North Carolina informed-consent law requiring doctors who perform abortions to display a sonogram of the fetus to the mother, describe it to her, and offer to let her hear the heartbeat. As J. Harvie Wilkinson wrote for the court, "The requirement is quintessential compelled speech." In that instance, the ACLU sided with the doctors—who, like photographers, "solicit customers from the general public and then claim to be engaged in autonomous expressive activity."

The flip side, of course, is that some on the right who object to compelled speech regarding gay weddings favor it regarding abortion.

And this is small potatoes compared to the implications of abortion rights for, say, welfare spending or health care. Take the recent case in which a pregnant Colorado woman was beaten and stabbed by another woman who then cut the baby out of her and tried to claim it as her own. The baby died, and the sickening case has prompted legislation that would add Colorado to the majority of states that make fetal homicide a crime.

Writing in The New York Times last week, law professor Debora Tuerkeimer argued that this was a very bad idea: "Granting personhood to fetuses makes women criminally responsible, not only for the life of the fetus, but also for its well-being. This is a particularly high burden. … Pregnant women have already been prosecuted for using drugs, refusing a cesarean section, having sex against a doctor's recommendation and attempting suicide. … Prosecutors could, in theory, use the notion of 'prenatal abuse' to pursue pregnant women who consumed too little folic acid; neglected exercise; gained too much or too little weight; continued on a course of anti-depressants; or had a stressful job. Under the mantle of fetal protection, pregnancy could become subject not only to criminal sanction but to pervasive state regulation."

All of this raises an obvious question: If a pregnant woman is not responsible for the welfare of the child within her womb—the child she willingly helped create—then why should that pregnant woman be responsible for the welfare of a child she has never met? Or a middle-aged man halfway across the country who just lost a job? Or an old woman five states away who needs a hip replacement? Indeed, why should anyone be responsible for anybody's welfare but their own?

And yet vast portions of the federal government are given over to forcing millions of people to guarantee the well-being of people they have never met, and whose needs (let alone lives) they had no role in creating.

Likewise, the logic of reproductive freedom implies that we should not impose conditions on pregnant women, such as requiring them to take folic acid, refrain from using drugs, and get sufficient exercise. They have no duty to do these things simply because it could affect the life to which they will soon give birth.

But if a pregnant woman has no such duties, then it is hard to see how she, or anyone else for that matter, has a duty to buy health insurance. Yet Obamacare forces everyone to buy health coverage (or pay a penalty). And it forces them to buy coverage not because their doing so will benefit others directly.

Rather, the reason is that if too many people fail to buy insurance, then the rules that force insurance companies to cover people regardless of pre-existing conditions could allow people to wait until they are sick before buying insurance. This would bankrupt insurance companies, and then the whole edifice of Obamacare would come crumbling down.

In short, the government can use force to make you buy health insurance so that other laws forcing insurance companies to accept all buyers will prove workable.

A great deal of conventional liberal wisdom about public policy grows out of a concern for equality, rather than liberty. While libertarians will argue that gay people should be free to marry whomever they choose, liberals are more likely to say marriage law should treat everybody the same.

Abortion rights is one of the few areas where liberals still make a first-principles defense of individual autonomy regardless of its consequences. But that approach doesn't square well with the progressive approach on so many other issues—and you don't have to look long or hard to see the cracks.