Mark published a post today that seemed to say they're taking Facebook in the opposite direction of Cake. We stand for better public conversation, they are going in the direction of more walled gardens.
Some people are tweeting that Zuck was against privacy before he was for it. My take is public discourse became bad enough on Twitter and Facebook that people are seeking shelter from the trolls. It isn't that people don't want public discourse and Internet fame, it's that they fear the trolls. When Reddit took steps to limit public trolling, it became much more popular.
I suspect he wants to put a bandage on their reputation for privacy. Perhaps talking about encryption will help. But...aren't many of Facebook's worst scandals from secret groups? They're under intense pressure to limit misinformation about vaccines, but those groups are thriving on Facebook because they are walled gardens.
As for privacy in these groups? It has become public sport to stealth into these groups, take screen captures of the things people say, and post them on public message forums. Since Facebook demands your real name, how private is that?