Following the 2016 US Presidential election, Facebook has faced persistent scrutiny from users and lawmakers over how it handles politics.

The most recent controversy involves Facebook's decision not to fact-check political ads, which it considers "political speech."

Facebook executives, including CEO Mark Zuckerberg and COO Sheryl Sandberg, have argued that the policy keeps Facebook from becoming the "arbiter of truth."

But in an interview with Sandberg on the Byers Market podcast published on Thursday, she argued that — even if Facebook wanted to — it would be impossible to fact-check political ads. "If you look at political ads and fact-checking political ads, that's really not something anyone is capable of doing," she said.

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Facebook is embroiled in yet another controversy, but this time it's not about your data: It's about foreign interference in American elections, and partisan politics, and freedom of speech.

It all stems from a relatively simple announcement Facebook made last year about how its advertising works: Facebook refuses to fact-check political ads that run on its platform.

"We don't fact-check political ads," Facebook CEO Mark Zuckerberg said in a wide-ranging speech at Georgetown University in mid-October. "We don't do this to help politicians, but because we think people should be able to see for themselves what politicians are saying. And if content is newsworthy, we also won't take it down even if it would otherwise conflict with many of our standards."

The position has proven controversial enough that Zuckerberg and Facebook COO Sheryl Sandberg have spent the last several months repeatedly defending it in interviews.

In Sandberg's latest interview, with NBC News' Byers Market podcast, she makes a new argument: Facebook is incapable of fact-checking political ads.

Sandberg said "there's no perfect answer here" in how the company treats political ads. Ruben Sprich/Reuters

"If you look at political ads and fact-checking political ads," she says, "that's really not something anyone is capable of doing. And we don't think we can make ourselves the arbiter of the truth."

Sandberg acknowledges that "there's no perfect answer here," and that Facebook is still evolving on the subject.

In the past, both Sandberg and Zuckerberg have argued two main points: Political advertising is equivalent to political speech, and therefore must be presented without censorship, and Facebook makes very little money from said advertising.

"We're not doing it because of the money," Sandberg said in an October 2019 interview with Bloomberg. "This is less than 1% of our revenue and the revenue is not worth the controversy."

Zuckerberg made a similar argument during an investor earnings call last year.

"In a democracy, I don't think it's right for private companies to censor politicians or the news," he said. "And although I've considered whether we should not carry these ads in the past, and I'll continue to do so, on balance so far I've thought we should continue. Ads can be an important part of voice — especially for candidates and advocacy groups the media might not otherwise cover so they can get their message into debates."

Mark Zuckerberg speaking at Georgetown University in October 2019. Andrew Caballero-Reynolds/AFP via Getty Images

Nearly as soon as Facebook began clarifying and defending its policy of not fact-checking political ads, criticism began.

Yaël Eisenstat, former head of global elections integrity ops at Facebook, published a scathing op-ed against the decision in The Washington Post. "The real problem is that Facebook profits partly by amplifying lies and selling dangerous targeting tools that allow political operatives to engage in a new level of information warfare," Eisenstat wrote in early November.

Additionally, a group of current Facebook employees sent an internal letter protesting the decision to Mark Zuckerberg.

"Free speech and paid speech are not the same thing," the letter reads, according to a copy of it published by The New York Times. "Misinformation affects us all. Our current policies on fact checking people in political office, or those running for office, are a threat to what FB stands for. We strongly object to this policy as it stands. It doesn't protect voices, but instead allows politicians to weaponize our platform by targeting people who believe that content posted by political figures is trustworthy."

Rep. Alexandria Ocasio-Cortez of New York and Sen. Elizabeth Warren of Massachusetts publicly backed the letter and the employees who wrote it.

"Facebook's own employees know just how dangerous their policy allowing politicians to lie in political ads will be for our democracy," Warren wrote. "Mark Zuckerberg should listen to them — and I applaud their brave efforts to hold their own company accountable."

Zuckerberg told Facebook employees last year that an Elizabeth Warren presidency would "suck" for the company. Justin Sullivan/Getty Images

If Facebook were to ban political ads, it would run into another issue — one that Twitter is almost certain to face: deciding what is and isn't "political" speech.

Zuckerberg highlighted as much during his speech at Georgetown.

"Even if we wanted to ban political ads, it's not clear where we'd draw the line," he said. "There are many more ads about issues than there are directly about elections. Would we ban all ads about healthcare or immigration or women's empowerment? If we banned candidates' ads but not these, would that really make sense to give everyone else a voice in political debates except the candidates themselves?"

It's a reasonable point — if Facebook were to ban "political" ads, it would have to spend a lot of time defining what is and isn't political speech. And then it would come under fire for policing free speech.

"There are issues any way you cut this," Zuckerberg said, "and when it's not absolutely clear what to do, I believe we should err on the side of greater expression."