Pope Francis has not been reluctant to offer his views on polarizing subjects, but on Wednesday, he waded into an issue involving two subjects on which consensus is almost impossible to find.

Pets and kids.

Speaking on parenthood during a general audience at the Vatican on Wednesday, Francis bemoaned the global decline in birthrates — what he described as a “demographic winter” — and was bluntly critical of couples who prefer to have pets rather than children.

People who have pets instead of children, the pope said, were being selfish, exhibiting a “denial of fatherhood or motherhood” that “diminishes us, it takes away our humanity.”

“Yes, dogs and cats take the place of children,” Francis said, laying out the harsh consequences of a childless future, including the inevitable drying up of pension plans. “Yes, it’s funny, I understand, but it is the reality.”

The reaction on social media was heated.

Several people pointed out that the pope had made a deliberate decision not to have children and should have little say on the matter. “Is the Vatican gonna pay daycare?” one Twitter user asked.

Others noted that Francis was failing to live up to his namesake, Francis of Assisi, patron saint of animals.

The pope had already signaled his kids-over-kibbles stance in a 2014 interview with the Rome daily Il Messaggero. When asked whether some in society valued pets more than children, he said that it was a reality that reflected a “sign of cultural degeneration.”

“That’s because an emotional relationship with animals is easier, more programmable,” he said at the time. He added, “Having a child is something complex.”

Pope Francis is not known to have kept pets in his apartment at a Vatican guesthouse. His predecessor, Pope Emeritus Benedict XVI, on the other hand, was such an avowed cat person that there is even a children’s book — “Joseph and Chico: The Life of Pope Benedict XVI as Told by a Cat” — told from a feline perspective. Another children’s book muses on a goldfish’s fondness for Benedict.

Agostino Paravicini Bagliani, the author of “Il Bestiario del Papa” (The Pope’s Bestiary), said that for many centuries popes had used animals, like the dove, “to create and confirm the authority and sovereignty” of the papacy, a reinforcement of its power. It was unclear, however, exactly how many popes had domestic pets, he noted; the most famous is Pope Pius II, who lived during the Renaissance and wrote about his dog, Musetta.

Other Renaissance popes also had pets, notably Paul II, who had a monkey; Sixtus IV, who had an eagle; and Leo X, who had a menagerie of exotic animals, including lions, leopards and bears, Mr. Paravicini Bagliani said.

He also cited a famous photograph of Pius XII with a goldfinch perched on his finger.

Pius VI kept a dog, Diana, at the summer papal residence in Castel Gandolfo.

Francis, too, has demonstrated that he respects and cares for animals.

In his 2015 encyclical on the environment, “Laudato Si’,” or “Praise Be to You. On Care for Our Common Home,” for example, he repeatedly pointed to interconnectedness of humans and all creatures.

“Because all creatures are connected, each must be cherished with love and respect, for all of us as living creatures are dependent on one another,” Francis wrote.

And during his papacy, he’s petted a number of animals, mostly dogs.

On Wednesday, Francis said the world was experiencing “an age of notorious orphanhood” that could be countered, in part, by caring for children, either through adoption or naturally. “It is riskier not to have them,” Francis said. “Think about this, please.”

One animal rights group said it wasn’t an either/or situation.

“It is strange to think that the pope considers love in our lives to be limited in quantity, and that giving it to someone takes it away from others,” said Massimo Comparotto, the president of the Italian branch of the International Organization for the Protection of Animals.

“Perhaps the pontiff is unaware of the enormous sacrifices that volunteers endure” to help save animals, he said in a statement. “Anyone who thinks that life is sacred loves life beyond species,” he said.