When it comes to curbing political manipulation on the internet, Mark Zuckerberg never seems to learn from his mistakes.

At a time when we need our political and business leaders to be at their best, the Facebook CEO once again stands as an embarrassment to the tech community. Zuckerberg has become an enabler of political manipulation who repeatedly chooses profits over principle.

A day of reckoning awaits the industry for Zuckerberg's refusal to properly police lies and threats of violence on his social network. We all value freedom of speech. But Zuckerberg fails to recognize it is not absolute — and that he has a responsibility to stop incitements of violence and disinformation.

President Donald Trump clearly crossed the line last on May 29, threatening George Floyd protesters when he said "when the looting starts, the shooting starts" on Facebook and Twitter.

Twitter CEO Jack Dorsey rightly intervened, flagging the post as incendiary and "glorifying violence." Then on Wednesday, Snap, which makes the Snapchat app, said it would stop promoting Trump's account because his public comments could incite violence. But Zuckerberg refuses to do the same, despite workers' insistence that the posts violated the company's policy against violent rhetoric.

After hundreds of Facebook employees staged a virtual "walkout" on June 1 in protest, Zuckerberg held an all-hands video meeting the next day and made what was, at best, a lame defense of his position. His basic position remains that he does not want to be an "arbiter of truth."

If he believes that, he needs to get out of the media business. Facebook is no longer just a platform. It is one of the world's largest purveyors of news. As such, it's Zuckerberg's responsibility to ferret out fact from fiction and determine when posts cross the line. Nearly three dozen of Facebook's earliest employees, including the company's first chief of communications, agree. They wrote an open letter to Zuckerberg on Wednesday saying he was betraying Facebook's ideals.

Meanwhile, Zuckerberg continues to rake in profits. The Bloomberg Billionaires Index recently ranked him the world's third-richest man with a net worth of about $87 billion, thanks in large part to Facebook's 2.5 billion monthly users.

And Americans are left to live with the disinformation and violence Zuckerberg perpetuates on his site.