NEW YORK – Some of Facebook’s former friends are starting to express some serious doubts about the social network they helped create.

Facebook exploits a “vulnerability in human psychology” to addict its users, Sean Parker, the company’s first president, said in a public forum last month. Chamath Palihapitiya, a former Facebook vice president who joined the company in 2007, recently told an audience at Stanford that the company is “ripping apart the social fabric of how society works.”

And Roger McNamee, a venture capitalist and early investor in both Facebook and Google, wrote that both companies “threaten public health and democracy” in an August USA Today op-ed.

It has been a rough year for the tech industry, especially social media companies. It opened with concerns about fake news and “filter bubbles” that can shield people from contrary beliefs, segued into pressure on Facebook and Twitter to clamp down on trolling and online harassment, and culminated with hearings into Russian agents’ alleged use of their platforms to meddle with the 2016 presidential election.

All of that, of course, came against a steady drumbeat of tweets from President Donald Trump, who used the service to praise his allies and castigate his foes, often in inflammatory fashion.

But the unkindest cut of all may have come from three people who helped build Facebook in its early days. In early November, Parker told the news site Axios that Facebook was built to answer the question, “How do we consume as much of your time and conscious attention as possible?” He called its stream of comments, “likes” and reactions a “social validation feedback loop that exploits how human brains work.”

A few days later, McNamee wrote another essay for the Guardian in which he argued that Facebook and Google have used “persuasive techniques developed by propagandists and the gambling industry,” combining them with modern technology to maximize their profits while pushing “appeals to fear and anger” and other material that reinforces filter bubbles and addictive behavior.