Earth Now Has 8 Billion Humans. This Man Wishes There Were None.

“It was very nice news for me that this kind of group existed, because one usually, with this kind of philosophy, feels alone,” said Mario Buenfil, 73, a water engineer in Mexico City who has been involved with the movement for 20 years.

Still, the words “voluntary human extinction” often elicit reactions of spluttering horror, and terms like “eco-fascist” and “Malthusian” are often lobbed at the group. John Seager, the president of Population Connection, a nonprofit that advocates population stabilization through voluntary means, likened it to a sideshow. Yet if the group’s provocative name and seemingly pugilistic stance suggest an embittered or even menacing founder, Mr. Knight seems anything but.

Tall and gentle, Mr. Knight comes across as clear-eyed and thoughtful, like a mash-up of Bill Nye and Fred Rogers. While Mr. Knight may be against the creation of more humans, he shows great compassion for the ones that already exist.

A high school substitute teacher for most of his working life, Mr. Knight is fondly regarded by students. He spends hours each Sunday morning picking up litter from the nearby main road. During an interview, he paused to appreciate two juicy garden spiders taking in the sun on gossamer webs spun between the hedges and lawn chairs. The sight was a cause for celebration, Mr. Knight said, after so many critters were killed during last year’s heat dome in the Pacific Northwest. A self-professed serial monogamist, he lives alone, but his girlfriend lives next door, and is fully on board with his cause.

“He doesn’t have a giant ego that he struts around with, he doesn’t try to argue with people,” said Marv Ross, Mr. Knight’s former college roommate and a longtime friend. “He was always about humor, to make it as fun as possible to get his message across, and I saw him do it many times. He’d deflect people getting upset with a joke or a smile.”

As a child growing up in a tolerant family in Oregon, Mr. Knight watched timber companies chop down the state’s forests. After being drafted in the Army during the Vietnam War (he served but never got deployed), he attended Oregon College of Education and joined the local chapter of Zero Population Growth, which cemented his resolve not to have children. “It was always because of the ecology, because of the damage that humans do to the environment,” he said.