Mr. Zuckerberg’s decision follows years of scandal for the social network, much of it originating from public sharing of posts. Foreign agents from countries like Russia have used Facebook to publish disinformation, in an attempt to sway elections. Some communities have used Facebook Groups to strengthen ideologies around issues such as anti-vaccination. And firms have harvested the material that people openly shared for all manner of purposes, including targeting advertising and creating voter profiles.

Even WhatsApp, which has long been encrypted, has grappled with the distribution of misinformation through its service, sometimes with deadly consequences.

All of that has put Facebook in the spotlight, which in turn has badly damaged the company’s reputation and created mistrust with users. Regulators have intensified scrutiny of Facebook’s privacy practices, with the Federal Trade Commission considering a multibillion-dollar fine against the company for violating a 2011 privacy consent decree. Last week, the agency said it would create a task force to monitor big tech companies and potential anti-competitive conduct.

Mr. Zuckerberg has repeatedly tried to rid Facebook of toxic content, disinformation and other problems. At one point, he emphasized prioritizing what friends and family shared on Facebook and de-emphasizing content from publishers and brands. He has also said that the company will hire more people to comb through and remove abusive or dangerous posts, and that it is working on artificial intelligence tools to do that job.

But none of those moves addressed the issue of public sharing. And in many ways, consumers were already moving en masse toward more private methods of digital communications.

Snap, the maker of the Snapchat app, has built a young, loyal audience by allowing people to share messages and stories for a finite period of time, for example. Other companies, like the local social networking company Nextdoor, focus on the power of group and community communications. And closed, private messaging services like Signal and Telegram have also become more prominent.

Evan Spiegel, chief executive of Snap, hinted at the problems that Facebook’s News Feed had created last week at a New York Times conference. Because of the way social networks had been constructed for people to publicly share content, he said, “things that are negative actually spread faster and further than things that are positive.” He later added, “You know, I certainly think there’s a lot of opportunity to sort of course-correct here.”