Mr. Matzneff was one of the leading writers to advocate the legalization of sex with children. In “Les Moins de Seize Ans,’’ or “Under 16 Years Old,” he writes, “To sleep with a child, it’s a holy experience, a baptismal event, a sacred adventure.” First published in 1974, it was republished in 2005.

Thinkers on the left, like Michel Foucault, Roland Barthes, Jean-Paul Sartre and Simone de Beauvoir, spoke in defense of the practice, or came to the defense of men accused of engaging in sex with people below the age of consent in France — which was and remains 15.

Libération, the newspaper co-founded by Sartre, championed pedophiles as a discriminated minority and ran personal ads by adults seeking children for sex.

The newspaper ran “revolting” articles about pedophilia into the 1980s, and its staff included activists who fought for the right to engage in “sexual relations with children,” its editor, Laurent Joffrin, acknowledged in an editorial this week, adding that the publication now opposed the practice.