A former Facebook employee has told US lawmakers that the company’s sites and apps “harm children, stoke division and weaken democracy”.
Frances Haugen, 37, claimed executives refuse to change because they put profits over safety.
She said responsibility for that lies right at the top with Facebook CEO Mark Zuckerberg.
Product manager turned whistleblower Ms Haugen heavily criticised the company at a hearing on Capitol Hill.
However, Facebook said she spoke about areas she has no knowledge of.
Ms Haugen testified to the Senate commerce subcommittee on consumer protection amid growing scrutiny of the social media giant and increasing calls for its regulation.
Facebook has 2.7 billion monthly active users, making it the world’s most popular platform.
Hundreds of millions also use WhatsApp and Instagram, which they also own.
But Facebook has been attacked for failing to protect users’ privacy and not doing enough to halt the spread of disinformation.
Speaking confidently at a charged hearing, Ms Haugen accused the company of being aware of apparent harm to some teenagers from Instagram and being dishonest in its public fight against hate and misinformation.
“Facebook’s products harm children, stoke division and weaken our democracy,” she said.
“The company’s leadership knows how to make Facebook and Instagram safer but won’t make the necessary changes because they have put their astronomical profits before people.
“Congressional action is needed. They won’t solve this crisis without your help.”
Ms Haugen said that while the company openly acknowledged that integrity controls were critical for internal systems that stoke the engagement of users, it failed to fully deploy some of those tools.
In dialogue with receptive Republican and Democratic senators, Ms Haugen explained the importance to the company of algorithms that govern what shows up on users’ news feeds.
She said a 2018 change to the content flow contributed to more divisiveness and ill will in a network ostensibly created to bring people closer together.
Despite the enmity that the new algorithms were feeding, she said Facebook found that they helped keep people coming back — a pattern that helped the social media giant sell more of the digital ads that generate the vast majority of its revenue.
Democratic senator Richard Blumenthal, the panel’s chairman, said: “It has profited off spreading misinformation and disinformation and sowing hate.
“Facebook’s answers to Facebook’s destructive impact always seems to be more Facebook, we need more Facebook — which means more pain, and more money for Facebook.”
Ms Haugen praised the massive outage of Facebook services on Monday, which affected users around the world.
She said: “Yesterday we saw Facebook taken off the internet.
“I don’t know why it went down, but I know that for more than five hours, Facebook wasn’t used to deepen divides, destabilise democracies and make young girls and women feel bad about their bodies.”
Facebook maintains Ms Haugen’s allegations are misleading and insists there is no evidence to support the premise that it is the primary cause of social polarisation.
Nick Clegg, Facebook’s vice president of policy and public affairs, said: “Even with the most sophisticated technology, which I believe we deploy, even with the tens of thousands of people that we employ to try and maintain safety and integrity on our platform, we’re never going to be absolutely on top of this 100% of the time.”
Mr Clegg said that was because of the “instantaneous and spontaneous form of communication” on Facebook, adding: “I think we do more than any reasonable person can expect to.”