I call bullshit on Zuckerbergs claim as birthday parties and group hangs streams are primarily with people you have direct relationship status with on Facebook and thus can be distingishued when distributed to users by Facebook as non-related users can have a delay added for review. This would at least greatly reduce the spread of said material to limited groups and if individuals within that groups choose to resubmit it to increase it’s reach a bit, they could be sued for actively and knowingly spreading illegal and harmful material.

Either Zuckerberg don’t want to move a finger, or he simply want regulators to regulate Facebook and other social media to create a higher barrier of entry into the social media market.