Speaking at an Axios event on Wednesday, Parker said he has evolved into “something of a conscientious objector” when it comes to social media, though he does still use his Twitter and Facebook accounts. Parker said that Facebook CEO and co-founder Mark Zuckerberg (among other social media entrepreneurs) understood that they were launching a website that could be addicting, “and we did it anyway.”

“The thought process that went into building these applications, Facebook being the first of them . . . was all about: ‘How do we consume as much of your time and conscious attention as possible?'” Parker told Axios.

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The tech billionaire, who is now the founder and chair of the Parker Institute for Cancer Immunotherapy, added that a widely used service like Facebook, which now has 2 billion monthly users around the world, “literally changes your relationship with society, with each other.” Parker also went on to call the social media giant “a social-validation feedback loop” that exploits a core vulnerability in the human psyche.

“God only knows what it’s doing to our children’s brains,” he said.

Parker, who also joked that Zuckerberg might block him on Facebook as a result of his candid remarks, was an early Facebook investor who made more than $2 billion when the company went public five years ago. He’s certainly not the only person criticizing Facebook (or other tech giants) these days. Zuckerberg’s company has caught flak recently over the spread of misinformation on the service, including as part of a concerted Russian effort to influence last year’s presidential election.