The major concern about a powerful new gene-editing technique that most people don't want to talk about

Scientists, bioethicists, and members of the public have descended on Washington, DC this week for an international meeting to discuss the ethics of a promising lab technique that lets scientists edit our genes.

The technique, known as CRISPR/Cas9, lets scientists cut-and-paste DNA inside cells to correct genetic defects or, potentially, add new capabilities. It offers enormous promise to improve our understanding of biology and to treat or even eliminate genetic diseases.

But there's a dark side to manipulating our genetics that few want to discuss: Eugenics, the racist practice of trying to "improve" the human race by controlling genetics and reproduction.

A disturbingly widespread practice

While eugenics is most commonly associated with Nazi Germany, it was alive and well in the US and in other countries well before World War II, Daniel Kevles, a historian of science at New York University, said during a talk at the gene editing summit on Tuesday.

"Eugenics was not unique to the Nazis. It could — and did — happen everywhere," Kevles said.

He and others worry that gene editing tools like CRISPR...