BUENOS AIRES, Argentina — Valuing truth over the right to privacy, Argentina's Congress has authorized the forced extraction of DNA from people who may have been born to political prisoners slain a quarter-century ago — even when they don't want to know their birth parents.

Human rights activists hope the new law will help find about 400 people stolen as babies, many from women who were kidnapped and gave birth inside clandestine torture centers during the 1976-1983 dictatorship. Thousands of leftists disappeared in what became known as the "dirty war" against political dissent.

Others see the new law as unacceptable government intrusion, legalizing the violation of a person's very identity. And as written, it could have much broader implications, enabling DNA to be sought from anyone whenever a judge determines the evidence to be "absolutely necessary."

Children of the "disappeared" were often given to military or police families considered loyal to the military government. Some have grown up not even knowing they were adopted until activists or judges announced efforts to obtain their DNA.

The project of the Grandmothers of...