An influential tech evangelist has called at the TED 2018 conference for an overhaul of Facebook and Google's business models.
Jaron Lanier, who is often referred to as a "father of virtual reality", told the Vancouver event that the two firms should let users pay for their services as an alternative to relying on ads.
"These companies need to change," he said.
But on Tuesday, Facebook's chief suggested this would not be popular.
"A number of people suggest that we should offer a version where people can not have ads if they pay a monthly subscription, and certainly we consider ideas like that," Mark Zuckerberg told a panel of senators in Washington.
"But overall, I think that the ads experience is going to be the best one.
"I think in general, people like not having to pay for a service. A lot of people can't afford to pay for a service around the world," Mr Zuckerberg added.
Mr Lanier was a frequent TED (Technology, Entertainment and Design) speaker during the 1980s.
But, he said, even then he had realised that "the technology we needed and loved could also be our undoing".
"We made a very particular mistake in the 90s when early digital culture had this lefty, socialist mission, which meant that everything on the internet must be available for free," he added.
That decision led directly to the advertising model that allows Google and Facebook to flourish, he explained.
"In the beginning it was cute but as computers became more efficient and algorithms got better, it can no longer be called advertising any more - it has turned into behaviour modification."
It was, he said, a "tragic mistake" rather than a "wave of evil", pointing out that he knew and loved many people working at the two tech empires.
But, he explained, the advertising model had led to addictive social media platforms that rewarded people for sharing their information with "likes".
He also claimed that Google and Facebook had become as "hooked and trapped" on the advertising model as their users.
"It is time to turn back the clock and remake that decision. Many people would pay for search and social networks," Mr Lanier said.
The virtual reality pioneer has for some years been a critic of the ways that technology and social media are shaping our lives.
And during his TED talk he suggested that his audience should "delete Facebook".
The social network has faced intense criticism over recent weeks in the wake of the Cambridge Analytica scandal, in which the Californian tech giant has conceded that it did not do enough to check that a political consultancy had deleted data harvested from its users.
Apple co-founder Steve Wozniak, the actor Will Ferrell and the car-maker Tesla are among those to have deleted or deactivated their accounts in the wake of the revelations.
The Whatsapp co-founder Brian Acton has also urged others to take similar action, despite the app now being owned by Facebook.
Mr Lanier said he had never had any social media accounts himself.
Mr Zuckerberg has said that while Facebook users are free to delete their data and quit his service, he has not seen them do so in "meaningful" numbers as a result of the privacy row.