"I don't actually believe Mark is sincere about what he has said year-to-date," McNamee said on CNBC's "Fast Money" on Tuesday.
Amid widespread criticism of the his company's role in the 2016 U.S. presidential election, Zuckerberg has said his personal challenge for 2018 is "to fully understand how our services are used, and to do everything we can to amplify the good and prevent harm." The Facebook co-founder said in January that the company made changes to that "reduced time spent on Facebook by an estimated 50 million hours every day to make sure people's time is well spent."
But McNamee, who co-founded investment firm Elevation Partners, has been increasingly in critical of the tech giant in which he invested years ago. On Tuesday he took it one step further, critiquing the CEO and his fellow executives for inability or unwillingness to fix the platform's misinformation problem. Facebook did not immediately respond to a request for comment
"Facebook right now is committing malpractice. As a shareholder, I'm terrified," McNamee said
McNamee has condemned the social media platform's addictive qualities, comparing its effects to nicotine, alcohol or heroin, prior even to Special Counsel Robert Mueller's indictment, which revealed the role of Facebook and other social media platforms in Russian misinformation warfare.
"And you have the head of advertising...suggesting the Russians weren't really trying to elect Trump. All they were trying to do is blow up America, like somehow that was an OK for Facebook to enable them to do," McNamee said, referring to Rob Goldman, vice president of ads at Facebook, who recently tweeted that sowing chaos, not electing Trump, was Russia's primary intent in infiltrating American social media networks.
Facebook's inaction will hurt not only hurt its brand, but its relationship with its home country, McNamee said — especially if Facebook continues to court markets, like China, where there is tight government control on news flow.
For Zuckerberg, McNamee has a piece of advice.
"Stop looking at China, stop looking at the future. Look here and now and help us prevent interference in 2018," he said.