Facebook's founder Mark Zuckerberg has said he does not think it is right for a company to censor politicians or the news in a democracy.
He was giving a speech in Washington DC following weeks of criticism over the firm's decision not to ban political adverts that contain falsehoods.
He added he had considered barring all political ads on his platforms.
But he said he believed the move would favour incumbent politicians and whoever the media chose to cover.
And Mr Zuckerberg said that even if he had supported the idea, it was not clear where his firm would draw the line.
Instead, he said, he had decided the company should "err on the side of greater expression".
"We're at another crossroads," he said.
"We can either continue to stand for free expression, understanding its messiness but believing that the long journey towards greater progress requires confronting ideas that challenge us. Or we can decide that the cost is simply temporary.
"The future depends on all of us," he added.
"And whether you like it or not. I think we need to recognise what is at stake, and come together to stand for voice and free expression at this critical moment."
Mr Zuckerberg referenced Martin Luther King Jr's imprisonment in Birmingham Jail, Alabama as an example of a previous backlash against free expression.
But the comparison drew criticism from the late civil rights campaigner's daughter, who said that disinformation spread by politicians had helped lead to her father's murder.
I heard #MarkZuckerberg's ‘free expression’ speech, in which he referenced my father. I'd like to help Facebook better understand the challenges #MLK faced from disinformation campaigns launched by politicians. These campaigns created an atmosphere for his assassination. pic.twitter.com/h97gvVmtSZ— Be A King (@BerniceKing) October 17, 2019
The speech was delivered at Georgetown University in Washington DC, after which the audience was invited to ask questions. However the question-and-answer section was not broadcast on a livestream provided to the public.
During his talk, Mr Zuckerberg also took the opportunity to make a dig at Chinese rival TikTok, which he said was censoring news of political protests.
And he suggested that his thwarted attempts to bring Facebook and Instagram to mainland China had worked out for the best.
"I wanted our services in China because I believe in connecting the whole world and I thought maybe we can help create a more open society," he explained.
"But we could never come to agreement on what it would take for us to operate there there, and they never let us in.
"And now, we have more freedom to speak out and stand up for the values that we believe in and fight for free expression around the world."
The event came three days after it emerged that since July, the Facebook chief executive had hosted private dinners at several of his homes to which he had invited conservative journalists, commentators and at least one Republican politician. These social events followed claims that the firm had shown bias against the right.
Facebook has also recently been attacked on the left, by two of the leading candidates in the contest to be the Democratic Party's candidate for the 2020 presidential election.
Last week, Senator Elizabeth Warren paid to run an intentionally misleading advert on its platform that claimed Mark Zuckerberg had personally endorsed Donald Trump for re-election.
She said she had done so in protest against the firm's decision to allow politicians to run ads containing" known lies".
"When profit comes up against protecting democracy, Facebook chooses profit," she claimed.
A spokesman for Joe Biden had previously criticised the firm for refusing to remove a video posted by Donald Trump's re-election campaign which promoted an unproven conspiracy theory involving the former vice president and his son.
"It is unacceptable for any social media company to knowingly allow deliberately misleading material to corrupt its platform," Mr Biden's press secretary said.
Mr Zuckerberg has also faced recent criticism from some of his Silicon Valley peers.
On Wednesday, Salesforce chief executive Marc Benioff described Facebook as being the "new cigarettes - it's addictive, bad for us, and our kids are being drawn in".
He also said that the company should be broken up to prevent it gathering so much data on the public.
"Why they can't say that trust is our highest value is beyond me," he added.
However, he has done so without mentioning the social media's firm by name.
I think Mark Zuckerberg may have prepared by watching Barack Obama's speeches.
The Facebook chief gave emphasis to his key points by delivering them in short bursts.
"At least we can... disagree!"
"That's what freedom of expression...is!"
I could almost hear the 44th president's accent.
There was a time, of course, when we thought Mr Zuckerberg fancied himself as a future president. But if it's no longer likely he'll lead the US, he perhaps sees a chance to lead on a defining issue: the changing nature of free expression.
Progressive regimes in history, he noted, have allowed more speech, not less. And, in what will play well in the corridors of western power, he repeated his view that restricting what people say on the internet - he meant Facebook - could cede power of the internet to China's tech giants rather than Silicon Valley's.
I often flip between thinking Mr Zuckerberg is right to say Facebook should take a light-touch approach to limiting what people can post, and seeing a chief executive who is reneging on a responsibility to fix his creation.
Ultimately, I believe, a big part of the problem isn't that people use Facebook to express themselves, but that it then tends to amplify the most outrageous, divisive content.
Even so, Mark Zuckerberg has achieved some important things today. First, he's clearly and openly asked for help.
And second, he's elevated the current debate on online speech into one of historical importance, a "crossroads" in line with the American civil rights struggle.
A hero of that movement, Congressman Elijah Cummings, died on Thursday - and Mr Zuckerberg paid tribute.
Cummings was a legendary advocate of free speech - but also a man who called loudly for Mr Zuckerberg to get his house in order.