When a doctored video of House Speaker Nancy Pelosi one altered to show the Democratic leader slurring her words began making the rounds on Facebook last week, the social network didn't take it down.
Instead, it "downranked" the video, a behind-the-scenes move intended to limit its spread.
That outraged some people who believe Facebook should do more to clamp down on misinformation.
Pelosi derided Facebook Wednesday for not taking down the video even though it knows it is false.
But the company and some civil libertarians warn that Facebook could evolve into an unaccountable censor if it's forced to make judgment calls on the veracity of text, photos or videos.
Facebook has long resisted making declarations about the truthfulness of posts that could open it up to charges of censorship or political bias.
It manages to get itself in enough trouble simply trying to enforce more basic rules in difficult cases, such as the time a straightforward application of its ban on nudity led it to remove an iconic Vietnam War photo of a naked girl fleeing a napalm attack.
(It backed down after criticism from the prime minister of Norway, among others.)
But as a result, he said, "any effort to clean up Facebook now would spark tremendous fury."