Many years ago I was part of a six-person debate panel on the Princeton University campus sponsored by Princeton’s famed debating club, the Whig-Cliosophic Society. Three people sat on the pro-abortion side, including two high-profile senior Princeton faculty—philosopher Peter Singer and biologist Lee Silver—and an experienced undergraduate debater named Emily Garin.

On the pro-life side sat I, a lowly part-time lecturer in Princeton’s Department of Politics; Daniel Robinson, a psychology professor from Georgetown totally unknown to most Princeton students; and a novice debater and freshman Whig-Clio member, Carlos Ramos-Mrosovsky. The arrangement looked like a set-up, with a weak team chosen to represent one side (pro-life), a much stronger team the other (pro-choice). Given that the vast majority of Princeton students were known to be on the pro-choice side of the controversy, it looked as if the debate would be a slam-dunk win for the abortion-rights people and a devastating loss for the babies.

From the start, however, the pro-life side began to capture the hearts and minds of listeners with a shared theme that resonated well with the largely college-student audience. A major purpose of law, we stressed, was to protect the lives and wellbeing of the weak and vulnerable. And who could be weaker and more vulnerable than the tiniest of human beings not yet out of their mothers’ wombs?

Daniel Robinson began with the vulnerability of the great apes in the African rain forests. We need laws—and enforcement of laws—to protect the diminishing ape population of Africa from illegal hunting and poaching. The audience clearly agreed with this.

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Carlos, our freshman partner, then chimed in with examples closer to home. We need laws, he said, to protect abused women from the violence of their abusing husbands and boyfriends, in addition to laws protecting gays and lesbians from those who seek to harm them through violence. This went over particularly well with the feminists and left-liberals in the audience.

I then added a third stratum of audience approval when I took up the issue of African slavery. We needed laws and constitutional amendments protecting black Africans seized from their homeland and forced to do slave labor in the New World by venal plantation owners. The slave-owners, I said, had no regard for the most basic human rights of their charges, and a civil war was fought partly to protect these rights.

As we progressed, it was clear our theme was persuading many of our listeners. The other side wasn’t helped very much by Lee Silver, who equated abortion with the destruction of the cells in his spit. Silver’s presentation began by his publicly expectorating into a petri dish. There are living human cells in this petri dish, he explained, and in the near future it will be possible through cloning techniques to grow fully formed human beings from these living cells. Yet we don’t think of these living human cells as human beings or human persons deserving of protection by the state. The destruction of early-term human embryos in their mothers’ wombs, Silver was suggesting, was little different from one expelling spit cells from one’s body and causing them to perish. Abortion should be thought of as no different from spitting.

Needless to say, Silver convinced no one by this comparison, but he did manage to reinforce the image of abortion-rights advocates as cold, insensitive, uncaring human beings.

Peter Singer’s presentation was a slight improvement, since it offered a well-articulated philosophical distinction between pre-personal and personal human life, with only the latter deserving a high level of state protection. The argument was too abstract for the intended audience, but it was at least coherent.

Singer, however, committed a strategic blunder when he turned toward our side of the panel and said, in a contemptuous tone, “If those on the other side really believed in a right to life they would be ethical vegetarians.” Singer had an established reputation as a leading “animal liberationist” and he hoped his taunt of the pro-lifers would win favor with the animal-rights sympathizers in the crowd.

But he chose the wrong right-to-lifers—Dan Robinson and I are ethical vegetarians. Dan took up the issue when his turn came for rebuttal. “I’m an ethical vegetarian,” he announced to the crowd, and then drew a laugh by adding (drawing attention to his oversized girth) “and as you can all see at great sacrifice to my personal wellbeing—I’m just wasting away!

The weakness of the other side was perhaps clearest when the undergraduate, Emily Garin, drew the most favorable audience response for her side. Her defense was nothing special—just the standard line that women are often hurt in many ways by laws forcing them to carry unwanted children. But her remarks contrasted with the philosophical abstruseness of Singer’s arguments and the crudity and callousness of Silver’s spit analogy. Fair-minded observers would probably have graded the three cases as B+, C+, and F, with the undergraduate clearly outshining the two senior professors.

At the start of my own talk, I threw the left-leaning Silver and Singer a knuckleball that completely threw them off-stride. “I am going to begin my remarks,” I said, “with what is essentially a Marxist argument.” There were some boos from the audience—Marxism is out of favor nowadays even among the student left. “Karl Marx,” I said, “got most things wrong” (some cheers went up). “But he understood better than most thinkers before or after him how people’s self-interest can warp their moral sense to the point that they are rendered incapable of discerning and acknowledging right from wrong.”

Marx’s biggest concern, I explained, was that material interests can distort our moral compasses. Drawing on the slavery analogy, I posed some simple questions: “Why did the Scarlett O’Haras and Rhett Butlers of the old South approve of the institution of slavery? Why did they think Africans so inferior to whites that it was morally acceptable to enslave them?”

The answer, I said, was simple: It was in their interest to believe these things. I went on: We human beings are very good at coming up with reasons and claims to justify what is in our interest to believe. So perverse is the human mind that we actually come to believe the sophistic arguments we tell ourselves when they reinforce our material or other vital interests.

The abortion issue, I said, is similar to the controversy over the rights and wrongs of slavery, since in both cases intense personal interests often dull the conscience. There are many out there, I said, who want to have sex but don’t want to have babies. They want to have sex because they find sex highly pleasurable. They don’t want to have babies because babies are enormously burdensome to take care of. So, like the plantation owners in the old South, they try to convince themselves that what is really a monstrous evil is no evil at all. Killing babies in their mothers’ wombs is no big deal. Human embryos are just globs of tissue without sentience or thought. Those who claim a human right to life for such entities just want to cause trouble.

I tried to reinforce the themes of “interest-driven corruption” and “false consciousness” by the old tag line: “A pro-choicer is a pro-lifer whose teenage daughter has become pregnant.” The saying is often used as a put-down of pro-lifers but what it really draws attention to, I said, is how weak and corruptible our moral sense and conscience really are. Self-interest produces willful blindness to evils that those less self-interested have no trouble seeing with the keenest of vision. The dairy farmers in Massachusetts, who had no personal interest at stake, had no trouble at all seeing the evils of plantation slavery in the old South.

When the attendees voted after the debate, the count was about evenly split; the pro-abortion side received just a few more votes than our side. Dan, Carlos, and I were ecstatic and considered the vote a great victory for our position, since we knew how widespread pro-abortion sentiment was among Princeton students. Many on the other side had to concede that at least on this occasion the pro-lifers had made a stronger case for their view than their opponents.

The more I reflect on this episode—which occurred more than a decade ago—the more I am convinced that the two points we drove home that night are the strongest that the pro-life movement has in winning over substantial numbers of young people, especially those on the secular left: first, we need laws to protect the weak and the vulnerable, and second, those who make light of killing a developing human embryo are engaging in willful blindness and an interest-driven deadening of their consciences. Both of these claims can still resonate on college campuses today. Marx and St. Francis make for a winning debate combination.