The Supreme Court on Tuesday upheld part of an Indiana law requiring aborted infants to be cremated or buried after an abortion. However, they sidestepped a larger ruling on abortion by deciding not to weigh in on whether a child can be aborted for their race, sex, or disability.

Justice Clarence Thomas wrote a concurring opinion, in which he addressed the pro-abortion movement’s well-known history with eugenics, and how the Court’s decision not to rule on the Indiana statute leaves an open question on whether eugenic abortions are protected by the Constitution.

The Indiana law in question, enacted in 2016 by former Governor Mike Pence, included a provision stating, “Indiana does not allow a fetus to be aborted solely because of the fetus’s race, color, national origin, ancestry, sex, or diagnosis or potential diagnosis of the fetus having Down syndrome or any other disability.”

These characteristics of an infant can be known early on in a pregnancy. Blood tests can now predict a baby’s sex at seven weeks. The law is intended to prevent mothers and abortion providers from using abortion as a tool of “modern-day eugenics,” as Thomas writes.

Thomas’ argument is two-fold. First, embracing abortion for the sake of eugenics was an endorsed practice and long-held belief of early 20th century progressive leaders. Second, with the development of more accurate prenatal tests, aborting children with unwanted characteristics is a modern threat disguised as “reproductive health services.”

Indeed, 21st century progressives often engage in a revisionist history of their early 20th century counterparts’ embrace of eugenics. But Thomas recounts the lengthy history Planned Parenthood founder Margaret Sanger had with the practice of population control. In 1921, she wrote that “the unbalance between the birth rate of the ‘unfit’ and the ‘fit’ [is] admittedly the greatest present menace to civilization” and that “the most urgent problem today is how to limit and discourage the over-fertility of the mentally and physically defective.”

Sanger was a featured guest of the Ku Klux Klan and a proponent of the forced sterilization program of the Nazi regime in the 1930s. She deemed the population of black Americans “degenerate and defective” and her clinics targeted black and immigrant communities like central Harlem in New York City.

Alan Guttmacher, president of Planned Parenthood in the 1960s and early 1970s who explicitly endorsed eugenic reasons for abortion, is also included in Thomas’ opinion. Guttmacher wrote that “it should be permissible to abort any pregnancy … in which there is a strong probability of an abnormal or malformed infant.”

The racist work of Planned Parenthood today is built on the foundational beliefs of their predecessors, Sanger and Guttmacher. Seventy-eight percent of Planned Parenthood clinics are located in minority communities. Blacks make up 12.1 percent of the U.S. population, but 35 percent of the country’s abortions. In his opinion, Thomas cites New York Department of Health data that states, “there are areas of New York City in which black children are more likely to be aborted than they are to be born alive—and are up to eight times more likely to be aborted than white children in the same area.”

Other modern uses of eugenics are rising around the world. In Iceland, nearly 100 percent of women who receive positive prenatal tests for Down syndrome abort their children. In the U.S. around 67 percent of women who find out their child will be born with Down syndrome opt to have an abortion, and in the United Kingdom, it’s around 90 percent.

In India and China, millions of female babies are aborted every year just because of their sex. The Invisible Girl Project estimates that 5 to 7 million sex-selective abortions are performed in India every year.

Thomas concludes that the increased use of eugenic abortions is exactly why Indiana passed a law protecting the unborn from discrimination, and exactly why the Supreme Court cannot ignore a ruling on the subject for much longer.

“Enshrining a constitutional right to an abortion based solely on the race, sex, or disability of an unborn child, as Planned Parenthood advocates, would constitutionalize the views of the 20th-century eugenics movement,” he writes. “In other contexts, the Court has been zealous in vindicating the rights of people even potentially subjected to race, sex, and disability discrimination.”