Zuckerberg said in Brussels on May 22 that while Facebook has brought in new features to connect people, it had become clear in the last two years that they "haven't done enough to prevent these tools from being used for harm".
But at a session where lawmakers got to ask all their questions in one go at the start, he annoyed them by batting many of them away - including on whether people can opt out of advertising and also on whether the U.S. giant is a monopoly that needs to be broken up.
"Some sort of regulation is important and inevitable", Zuckerberg said, but he echoed calls in the United States that innovation should not be stifled.
The European and US 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.
In his responses to questions, which spanned just 25 minutes of the brief meeting, Mr. Zuckerberg apologized once more for the Cambridge Analytica controversy and said Facebook had been too slow to recognize Russian interference in the 2016 US presidential election.
"It's time to consider breaking the Facebook monopoly, because it's already too much power in only one hand", one MEP said. Weber asked. "Can you convince me not to?"
Zuckerberg used his opening statement to apologize to the committee much like he had in the US.
Zuckerberg didn't rise to the bait, but instead pointed out that the company faces stiff competition.
On whether or not Facebook is a monopoly, the CEO said that Facebook exists in a competitive space where it is constantly forced to update its services to keep up with competitors. "The average person uses about eight different tools for communication - it feels like there are new competitors coming up every day".
Al Jazeera's Jonah Hull, reporting from Brussels, said that Zuckerberg provided "pretty un-enriching" responses to the MEPs' questions. I think the question is what is the right regulation ... Antonio Tajani, president of the European Parliament, also reassured the MEPs that their questions would be properly addressed.
"He's not obliged to come". Belgian Philippe Lamberts said as the meeting was almost over.
Guy Verhofstadt, leader of the Alliance of Liberals and Democrats for Europe, who was perhaps the most feisty of the lawmakers, asked whether Facebook would compensate its users, a provision included in the GDPR (a common argument among Facebook observers is that users are actually free laborers for the company, and advertisers are the real customers). "This wasn't a mandatory hearing".
"Historically, of course, it's true that through Facebook and other forms of social media, there's no way that Brexit or Trump or the Italian election could have ever possibly have happened", Farage told Zuckerberg at a hearing before the European Parliament on Tuesday.
The 34-year-old CEO spent about 10 hours testifying in front of the US Congress in April.
"Mr. Zuckerberg's apologies are not enough", Tajani said at a later news conference.
He will also apologise for failing "to take a broad enough view" of the company's responsibilities, "whether it's fake news, foreign interference in elections or developers misusing people's information". I am very sorry! European lawmakers hammered the executive with more incisive questions than during his congressional hearings last month.
Damian Collins, the chair of the British inquiry that has repeatedly asked Zuckerberg to appear before parliament, described the session as "an hour of questions, followed by a lengthy statement from Zuckerberg, with all hard questions dodged".