Ms. Bass, who is organizing a Knight Institute symposium in October on tech giants, monopoly power and public discourse, said she worried that popular enthusiasm for aggressive regulation of speech on the platforms could get out of hand. She worries that now arguments for moderating speech are coming from groups that once stood against government intervention. [Update, July 15, 2019: After this article was published, Ms. Bass said her Knight Institute symposium was being moved from October to November.]

“The idea that these platforms should be pretty tightly regulated on what speech they can host is not a traditional conservative argument,” Ms. Bass said. “This has all been a real whiplash.”

A case in point: On Thursday , The Washington Post published an essay by Charlie Kirk, the president of Turning Point USA, a group for young conservatives, proposing that digital platforms be regulated the way publishers are.

“Fighting back against private companies with governmental action is a politically and ideologically fraught idea for those of us on the right,” he wrote. But he went on to add, “There is now ample reason to believe the market’s normal corrective powers are being blocked by anti-competitive forces.”

Traditional conservatives said they were feeling the whiplash. James Pethokoukis, an analyst at the American Enterprise Institute, a pro-market think tank, was at a party this spring that included Republican donors in Washington when the conversation took a turn toward big tech companies.

“They were talking about breaking them up, turning them into utilities,” Mr. Pethokoukis said. “It’s a breathtaking change from even a year ago.”

He was shocked. To him these companies were American jewels and some of the best bulwarks against rising power abroad. He has since been writing against the movement with pieces like “The Astonishingly Weak Antitrust Case Against Facebook, Google, and Amazon.”