Late Sunday, Apple — which has often tried to stake out moral high ground on contentious debates — removed Infowars podcasts from iTunes. After seeing the news, Mr. Zuckerberg sent a note to his team confirming his own decision: the strikes against Infowars and Mr. Jones would count individually, and the pages would come down. The announcement arrived at 3 a.m. Pacific time.

In the days that followed, other platforms — YouTube, Pinterest, MailChimp, and more — said they, too, were banning Infowars. The notable exception was Twitter, which decided not to ban the site or Mr. Jones. The company’s chief executive, Jack Dorsey, tweeted a veiled shot at the way his rivals handled the situation.

“We’re going to hold Jones to the same standard we hold to every account, not taking one-off actions to make us feel good in the short term, and adding fuel to new conspiracy theories,” he said.

Now, cut off from most of his audience, Mr. Jones will have to chart a new course. He has already stepped enthusiastically into a role as a free-speech martyr. (After the ban took effect, Infowars slapped a “censored” label on its videos and launched a “forbidden information” marketing campaign.) And conservatives — and even some free-speech advocates on the left — worried that social media companies may be entering a new, censorious era. Senator Ted Cruz, the Republican from Texas, paraphrased the famous Martin Niemöller poem about German accommodation of Nazism: “First, they came for Alex Jones.”

Social media executives have a history of going to great lengths to assuage fears of anti-conservative bias, and this week was no exception. On Thursday, Richard Allan, a Facebook vice president of policy, published a blog post about the company’s commitment to free speech. With the exception of violent threats and hate speech, he wrote, “we lean toward free expression. It’s core to both who we are and why we exist.” Mr. Dorsey also appeared on Sean Hannity’s radio show, where he gave reassurances that Twitter does not discriminate against conservatives.