One member of Parliament said he had asked "six yes or no questions without a single answer".
As the session drew to a close, Antonio Tajani, the president of the European Parliament, was forced to contend with MEPs who were angry that Zuckerberg had not been pressed to answer numerous questions put to him.
The setup of the meeting was largely to blame. The lawmakers were given three minutes each to ask their questions one after another.
"I don't think the question is whether or not there should be regulation".
This is a standard format for meetings of the group, according to the parliament's spokesperson.
The Silicon Valley executive once again apologized for not doing enough to protect user data - an apology he has offered repeatedly to government leaders and users since the Cambridge Analytical scandal broke.
You have to ask yourself how you will be remembered. "Maybe you have less control or no control of your own company", he said, noting that Zuckerberg has apologized "15 or 16 times", and yet the company's problems persist.
Parenthetically, in a study of 50 online publishers released in March, The Western Journal concluded that modifications to Facebook's news feeds have adversely affected conservatives' market share far more than liberals.
"Unfortunately the format of questioning allowed Mr Zuckerberg to cherry-pick his responses and not respond to each individual point", said Damian Collins, chair of the UK Parliament's Digital Culture Media and Sport Committee.
Zuckerberg meanwhile admitted that Facebook had been "too slow to identify Russian interfering" in the 2016 USA presidential ballot, but was working with European governments for future elections.
He conceded that Facebook hasn't "done enough to prevent these tools from being used for harm...and that goes for fake news, foreign interference in elections and developers misusing people's information".
Zuckerberg said investments in security would significantly impact Facebook's profitability, but "keeping people safe will always be more important than maximising our profits". "Mark Zuckerberg is getting away without responding to citizens' concerns", Udo Bullmann, the leader of the Socialists and Democrats group in the European Parliament, tweeted later.
The chorus of frustration underscored the European Parliament's limited powers, and exacerbated a standoff between the EU and the world's largest social network over data collection practices that have sparked a global scandal over alleged privacy infringements. "From where I sit, it feels like there are new types of media all the time", he said.
As Zuckerberg moved to wrap up his time, MEPs attempted to keep him talking with direct questions about shadow profiles and advertising opt-outs, which led to a lot of deer-in-the-headlight looks from Zuck.
In an effort to combat "fake news", Zuckerberg said Facebook has attacked the economic incentives for spammers to traffic in sensational clickbait, and it's combatting phony accounts used to spread bad information - removed some 580 million fake accounts in the first quarter of the year.
By design, though, Zuckerberg answered all of lawmakers' questions at once at the end of the hearing.
Daniel Ives, an analyst with GHB Insights, wrote in an investor note Tuesday that he expects "more back and forth between the European Union and Facebook over the coming weeks".
The European and USA inquiries concern the same fundamental questions about the social media giant, triggered by the news that Facebook permitted Cambridge Analytica to harvest the private data of 87 million users and that Facebook failed to take action when it became clear in 2016 that foreign actors were using its platform to spread disinformation and undermine democratic processes. Up to 2.7 million of those Facebook users were based in the EU.
"Are you telling the truth, in fact, to us?" he asked the Facebook CEO about the company's pledge to adhere to Europe's privacy laws.
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