Damian Collins MP, chair of the British Parliamentary DCMS committee which has repeatedly asked Zuckerberg to testify in the United Kingdom, only to be snubbed, responded angrily, blasting the event as a "missed opportunity".
Mr Zuckerberg was subjected to an 80-minute hearing, though was only left seven of those minutes to answer the questions put to him by the MEPs.
But a confrontation was triggered after he failed to respond to an inquiry from Syed Kamall, a conservative British politician, who had asked about "shadow profiles", a term used for private profiles of both users and non-users based on contact information gleaned from Facebook users' phones and inboxes. The policymakers wanted answers about the Cambridge Analytica data scandal-in which, lest we forget, the data broker gained access to 87 million Facebook users' profiles.
However, he only agreed for it to be livestreamed on Monday after initially insisting on it being behind closed doors. The main question was whether Facebook has taken the necessary steps to address the new regulations. Zuckerberg was given time to answer them in the end.
"We weren't prepared enough for the kind of coordinated misinformation operations that we are now aware of", Zuckerberg said, referring to Facebook's role in interference in the 2016 USA 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.
"That was a mistake, and I'm sorry for it". "I got not a single answer". Zuckerberg commented on a number of issues, including Facebook's new effort to combat fake news, moderating inappropriate content and investigating third-party app developers to prevent incidents like Cambridge Analytica from happening again.
The leaders of the Parliament's political factions had prepared for the encounter, hoping to corner the CEO on specific issues including privacy, competition and election manipulation.
"Whilst this was another important step in drawing attention to this very serious situation, unfortunately the format was a get out of jail free card and gave Mr. Zuckerberg too much room to avoid the hard questions". To which Zuckerberg responded with a slightly dismissive, "I'll make sure we follow up and get you answers".
While Zuckerberg ducked some of the tough questions posed by the lawmakers, he did apologize for Facebook policies that allowed the spread of fake news during the 2016 USA presidential election and the British "Brexit" referendum.
"Will you guarantee that no manipulation from foreign and hostile interference ... on your platform can happen?" asked Bullmann. The new General Data Protection Regulation taking effect this week governs how internet companies can collect personal data, with all users needing to be informed about practices and to give permission for their data to be shared.
EU Justice Commissioner Vera Jourova recently paid Zuckerberg a backhanded compliment for having admitted that the Facebook scandal showed the need for strict new rules despite the reluctance of U.S. internet giants.
Zuckerberg also fielded questions from France's Front National and the U.K.'s Nigel Farage, the architect of Brexit, over a perceived bias. Zuckerberg immediately trotted out his dorm room story of not expecting Facebook's current duty to safety and democracy, and repeated his pledge to broaden the company's responsibility.