Mr. Williams is only a partial heretic. He acknowledges that social media companies have not done enough to promote high-quality content, but he also blames publishers for amping up sensationalism in order to increase their traffic. And when I asked if he agreed with Mr. Zuckerberg’s recent statement that “the world would lose if Facebook went away,” he demurred.

“I honestly don’t know my answer to that,” he said. “I think it’s probably right.”

But if Mr. Williams isn’t ready to denounce social media, he is at least muting its effects in his own life. He still uses Twitter, but he has turned off most mobile notifications, and he tries to leave his phone behind when he’s with his friends or his kids. He is reading less daily news these days, he said, and more books and long-form articles.

“That’s been healthy for me,” he said. “I feel the effects of that.”

Listening to an architect of the fast-twitch internet extol the benefits of books and magazines is a little odd, like watching Chef Boyardee open a farm-to-table restaurant. But Mr. Williams is not alone among tech leaders in his quest for a slower and more balanced media diet. (Mr. Dorsey, who has been Twitter’s chief executive since 2015, went on a 10-day silent meditation retreat in December.)

Whatever you think of his lamentations, give Mr. Williams credit for this: As a billionaire who has already cashed out a big chunk of his tech wealth, Mr. Williams could be waxing philosophic from a tropical cabana. Instead, he is rolling up his sleeves and trying to fix things.