President Trump’s historic presence at Friday’s March for Life will give significant attention to this annual event. It’s important, then, for people to understand why those who oppose abortion continue to fight.

The March for Life occurs every year on or close to the date the Supreme Court issued its ruling in Roe v. Wade, the decision that mandated legal abortion throughout the United States. Every year since then, hundreds of thousands of pro-lifers come to Washington to hear speakers, to rally and then to march from the Mall to the Supreme Court.

The march is nearly 50 years old, and pro-life sentiment shows no signs of receding. Indeed, poll data show that opinions about legal abortion have remained very stable since Roe. Abortion stands out from other so-called social issues, such as same-sex marriage, for which liberal or non-traditional views have seen a marked increase in support. This is because opposition to abortion is perhaps the only traditional social-issue viewpoint that fits neatly into the modern moral framework that prioritizes individual rights and choice.

It fits because pro-lifers emphasize the inherent dignity and worth of every living human being. As embryology textbooks tell us, the child who lives inside the woman is as much a human as the mother herself. That’s basic science. From the moment of conception, that unborn child possesses its own unique, human DNA. Whether it can be developmentally labeled as a zygote, an embryo or a fetus, it is scientifically, biologically distinct from the woman who carries it.

Those who support legalized abortion label themselves “pro-choice” because they would rather focus on the effect that carrying this separate human will have on the mother’s life. The unborn child is utterly dependent upon the mother’s body to provide it with the nutrition she or he needs to grow. Pro-choice advocates say the mother should decide whether she wants to allow her body to be used in such a manner, and that she alone — in consultation with her doctor — should decide whether allowing this is in her physical or emotional interests.

Pro-lifers do not disagree with the moral premise of this argument insofar as it applies solely to the woman’s body. They do, however, take issue with the idea that the unborn child is simply part of the woman’s body. It is not; it is a separate — even if radically dependent — human being. Recognizing that there are two humans involved in this process is absolutely fundamental to making a fully informed moral decision about abortion’s legality.

The difference between these two points of view comes into clear focus when we discuss the issue of late-term abortion. An unborn child can survive without being connected to a woman’s body at some point around the 22nd week of pregnancy. The rate of survival for babies born prematurely at that time is around 10 percent, but it increases dramatically for every day the child is carried after that. By the 25th week, the survival rate is above 70 percent, with some studies showing it closer to 90 percent. A pro-lifer sees these data and concludes that we have a moral obligation to save a fetus who could live with medical assistance. In this view, medical professionals have the same obligation toward this person as they would have toward any other living person who needed their care to live.

The pro-choice movement, however, increasingly disagrees with this point. They support bills in states that permit abortions to be carried out after the 24th week of pregnancy. They have also opposed efforts to require doctors to provide medical care for infants born alive after an abortion attempt. For them, it seems the mother’s choice trumps the child’s ability to live even when competent medical care could save that child’s life.

An honest debate over abortion’s legality would start with the simple recognition that two human beings are involved. People can disagree over when and under what circumstances legal protections ought to extend to the child’s life. Indeed, pro-lifers disagree themselves over this issue, with many saying that abortion should be allowed in cases of rape, incest or when the life of the mother is at stake, while others say that even the horrors of rape and incest cannot justify the taking of the child’s life. This debate takes place, however, beneath a moral framework that recognizes the scientific fact that at every stage of development the unborn child is uniquely and distinctly human.

The annual March for Life exists to remind Americans of this simple fact. It took civil rights marchers decades to persuade Americans that blacks were fully Americans and deserved the same legal rights as whites. In time, pro-lifers believe Americans will come to see that the beauty of life exists well before the moment of full-term delivery. We, too, shall overcome.

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