Elevation Partners' co-founder told CNBC's "Squawk Alley" on Wednesday that the business model these companies have adopted has serious consequences for users and the public at large.
"If you're trying to maintain attention, if you're fighting for a share of 24 hours in peoples' lives, the big issue is you have to keep escalating. It turns out the way you keep people's attention is you either scare them or you make them angry." He compared the effects of Google and Facebook to nicotine, alcohol or heroin.
Still, the people running the companies aren't "terrible" people, McNamee said.
"I don't think they are consciously doing bad things. I think what happened was they each adopted an advertising-based business model that essentially encouraged engagement," McNamee said.
In a USA Today opinion piece this week, McNamee said he's become "terrified" of damaging, unhealthy practices of these companies, such as "addictive behaviors that compel consumers to check for new messages, respond to notifications, and seek validation from technologies whose only goal is to generate profits for their owners."
He admited he "profited enormously" from early investments in the companies, and said that if he could go back to his early days as a Facebook advisor, he "would try a lot harder and a lot sooner to get them to diversify their business model, so it was not so dependent on anger and fear."
"When I invested in Facebook in particular, where I was very, very active, it never occurred to me that anything bad could ever happen from people sharing photographs and stories about family," McNamee said.
McNamee said events like Brexit and the U.S. election should cause Facebook and Google users to pause and debate the effects that these services could have on children.
"These systems are open, anyone can use these systems to manipulate public opinion because the ad models essentially encourage this exploitation of peoples emotions," McNamee said.
"Is this really something we want? Because these companies can afford to do this differently," McNamee said. "They are allowed to run experiments across a population of 2 billion people without being accountable for what happens."
Neither Facebook nor Google immediately responded to CNBC requests for comment.