Zuckerberg has ordered his staff to turn over thousands of advertisements to Congress, after the company determined that an estimated 10 million people saw Russian ads on "divisive" social issues. He also shared a 9-point plan for Facebook to "protect election integrity and make sure that Facebook is a force for good in democracy."
But Zuckerberg shifted his tone over the past year. He initially said it was "crazy" that Facebook had influenced the election.
"I am quite certain that it never occurred to Facebook that a foreign country was going to come in and mess with our elections," McNamee said. "But the reality is that they also had a business model that said, 'It's not our responsibility what people do on the platform.' And I think that was wrong."
McNamee called for Zuckerberg to "come clean" in a USA Today op-ed this week, writing that the co-founder and CEO should testify before Congress and inform each user whether they were targeted by any "malicious" Russian actors.
"I believe it's very, very important for Facebook to contact every single person that was touched by Russian propaganda ... and explain that they — which is to say Facebook and the users — were misled by the Russians," McNamee said. "And to do this in a way that is extremely personal, at the individual level. Because it's the only way that people are going to believe that what I'm talking about right now isn't fake news."
He later added: "It's one of those things they just have to do as patriots."
McNamee, managing director and co-founder of Elevation Partners, has recently become outspoken on the perils of attention-seeking apps such as Facebook and Google, writing that they "exploit human nature" and create "addictive" behavior. (Facebook and Google did not respond to CNBC's request for comment at that time.)
But when it comes to the election, McNamee has homed in on Facebook.
"They are all to blame; the difference is that the Facebook platform just had more impact," McNamee said. "It's bigger. It's much more personal. People are using it much more for convening around ideas."
McNamee warned that Facebook's brand, beyond political advertising, may be put at risk by the company's handling of the Russian ads.
"Facebook is messing with their most important aspect, which is trust. The brand is based on trust between the platform and the users who are on it," McNamee said, adding: "They may get away with this, but they shouldn't feel good about it if they do. Because the country's been harmed by this. And it's still going on ... we have to watch out."
— CNBC's John Shinal contributed to this report.