Last week many of us were disgusted to learn Planned Parenthood is harvesting and selling body parts from aborted children. As the largest provider of abortion in America, Planned Parenthood is part of the problem, on the “supply” side. But as we all learned in Econ 101, there’s both supply and demand. What’s behind the demand for abortion? A major factor is the breakdown of the family. And the Supreme Court’s ruling to redefine marriage is only taking us further down that road, putting even more unborn children at risk. After all redefining marriage redefines parenthood.

The best protectors of unborn children are a strong marriage culture and people who take the virtue of chastity seriously. But the new consent-based view of marriage reduces marriage to a mere contract and it makes a culture of chastity harder to foster. And, as I explain in my new book, without a culture of chastity, we will never have a pro-life culture.

Indeed, both the pro-choice movement and the movement to redefine marriage reduce human community to contract and consent and limit our obligations to other human beings to those we have freely chosen. Consider their slogans: “My body, my choice.” “I consented to sex, not to having a baby!” “Love makes a marriage.” “Marriage should last as long as the love lasts.” They all reflect the belief that consenting adults should do whatever they want to do, a belief that puts adult desire before the needs of children. And weakening marriage will lead to a culture with more nonmarital sex, thus more nonmarital pregnancy, and sadly more abortion.

Redefining marriage will also increase the use of assisted reproductive technologies. The movement to redefine marriage insists that there are “no differences” between the marital union of husband and wife and the union of two people of the same sex, yet a same-sex couple cannot conceive a child naturally. To achieve full “marriage equality,” then, it will be necessary to turn to modern technology. Same-sex couples must use assisted reproductive technologies—with the assistance of sperm donors, egg donors, surrogate wombs, etc.—so they can “have children of their own.”