WASHINGTON — Mark Zuckerberg today gave a full-throated defense of Facebook as a champion of free expression, fighting the idea that the social network needs to be an arbiter of speech as it has faced blowback for leaving up false political ads going into the 2020 presidential election.

In a winding, 35-minute speech at Georgetown University’s Gaston Hall — where presidents and foreign heads of state have delivered addresses — the Facebook chief executive said the social network had been founded to give people a voice and bring them together and that critics who had assailed the company for doing so were setting a dangerous example.

To make his case, Zuckerberg invoked Frederick Douglass, Martin Luther King Jr., the Vietnam War and the First Amendment. He contrasted Facebook’s position with that of China, where Beijing controls and censors speech and where he tried unsuccessfully for years to enter to turbocharge his company’s business.

“People having the power to express themselves at scale is a new kind of force in the world — a Fifth Estate alongside the other power structures of society,” Zuckerberg, 35, said.

He added that despite the messiness of free speech, “the long journey towards greater progress requires confronting ideas that challenge us. I’m here today because I believe we must continue to stand for free expression.”

The address by the tech billionaire was an unusually public doubling down on free expression online as debate over that stance has ramped up.

It was a sign that Zuckerberg was going on the offense against critics who have accused Facebook of being an amplifier of disinformation, hate speech and violent content.

Zuckerberg made his stand as Facebook has grappled with a firestorm over political speech in recent weeks.

Last month, the company unveiled a sweeping policy in which it said it would not moderate politicians’ speech or fact-check their political ads because the comments by political leaders, even if false, were newsworthy and in the public’s interest to hear and debate.

That quickly drew condemnation. Sen. Elizabeth Warren, a leading Democratic presidential candidate, accused Facebook of being a “disinformation-for-profit machine.”

Marc Benioff, chief executive of software company Salesforce, said the social network “needs to be held accountable for propaganda on its platform.” And civil rights groups censured the company for allowing lies and falsehoods to appear on its site.

Today, Zuckerberg’s speech was also lambasted.

“Zuckerberg attempted to use the Constitution as a shield for his company’s bottom line, and his choice to cloak Facebook’s policy in a feigned concern for free expression demonstrates how unprepared his company is for this unique moment in our history and how little it has learned over the past few years,” said Bill Russo, a spokesman for Joe Biden’s presidential campaign.

Facebook’s position on political speech is part of a growing divide between social media companies and traditional media companies. Twitter, too, has said it will not remove accounts of politicians who appear to violate its policies against violent speech because the posts add to discourse.

In contrast, traditional media companies — including cable channels like CNN, MSNBC and CNBC — have taken a harder line by declining to air political ads with false content.

Facebook’s policy on political speech was put to the test this month when the Trump campaign released a 30-second video ad that falsely claimed Biden committed corrupt acts in Ukraine. The ad played across social media outlets and on some broadcast networks; CNN and NBCU declined to air it because they said the ad violated their standards.

When Biden’s campaign asked Facebook to take down the false ad, the social network refused.

Warren later dared Facebook by deliberately creating an inaccurate political ad that said Facebook and Zuckerberg were backing Trump’s reelection, even though neither Zuckerberg nor his company have announced their support of a candidate.

“We decided to see just how far it goes,” Warren wrote on Twitter of her move.

Civil rights groups said they were stunned by how hands-off Facebook was being on political speech. By giving politicians free rein to post any material — even lies — that potentially sets up the social network for more disinformation efforts before the 2020 election, they said.

Vanita Gupta, president of the Leadership Conference on Civil and Human Rights, a coalition representing 220 civil rights groups, said she spoke to Zuckerberg last week to express alarm about the policy. She said he told her the public could make its own determinations about false statements and racially divisive content from politicians.

“Mark Zuckerberg is co-opting civil rights history to try to justify Facebook’s policies that do long-term damage to our democracy,” Gupta said. “The company is in denial about what’s happening.”

Neil Chilson, a senior research fellow at Stand Together, an organization within the Koch Network, said Facebook’s free speech position was “a very reasonable policy choice.” When Trump speaks, reporters then fact-check what he says, showing “that the cure to a politician’s misstatement is more speech, not to shut it down,” Chilson said.

Zuckerberg decided in recent days to publicly speak at Georgetown University as the debate over Facebook’s position on political discourse became louder. On Wednesday, he posted on Facebook that he was writing a speech that was “the most comprehensive take I’ve written about my views, why I believe voice is important.”

He will continue his public offensive Friday, when he plans to be interviewed by Dana Perino of Fox News.

Next week, he will be in Washington for a hearing on the company’s cryptocurrency project, called Libra. It will be his second time testifying in front of Congress after April 2018, when he answered lawmakers’ questions on Facebook’s treatment of user data.

In an interview at Facebook’s Silicon Valley headquarters Tuesday, Zuckerberg laid out more of the reasoning behind his speech. He repeatedly cited Facebook’s role as an American company and how it would be viewed over time.

“Today, the state of the global internet around the world is primarily defined by American companies and platforms with strong free expression values,” he said. “There’s just no guarantee that will win out over time.”

In his speech, he said he had considered banning political ads from Facebook. But he said political advertising could be considered part of speech and that the slope of deciding which issues were political and which were not would be too slippery to navigate. He added that political ads were a negligible amount of Facebook’s $55.8 billion in annual revenue.

Zuckerberg acknowledged in the interview that his position would not satisfy everyone. But he said he wrote the address to lay out his broader views and how he wanted his company to operate long into the future — including the far-off day when he is no longer running Facebook.

“I hope this is a moment for us to put our place in history in perspective,” he said.