Is Meta not the absolute antithesis of privacy? The complete polar-opposite of what people have tried to achieve with the fediverse? One of the main things they are trying to move away from?
Seems like a very strange decision here - "letting the fox into the hen house".
Because (a) it keeps regulators off their back, (b) they can monetise content generated in other apps and (c) it keeps the competition on a level playing field which plays to their strengths.
The decentralization forces some things to be fully public, such as your likes, who upvotes what etc
Plus from a legislation standpoint, you lose some of your rights out there - like the right to be forgotten. It's impossible to enforce GDPR on ActivityPub.
It's a weird middle-seat where on one hand, the fediverse won't start asking you for your name or to get a picture of you holding your ID, but on the other, at least when Facebook trains its models on the stuff you post, they'll tell you about it in their user agreement.
There's also the legal approach: keep data public but forbid usage for unauthorized purposes. Then at least the big public companies might not put their hands in it (at least not directly). But it could still be leaked and widely used by nefarious or shady actors.
In any case I think a more well thought out or just better informed distinction between public posts and private ones would be very useful (it appears currently in Mastodon you need to have a 'locked account' to post followers-only posts; I don't know if data goes to other servers for private posts?). If you post something anyone can see on the internet, there's a significant limit to how much the law or any technical solution could protect you. The right solution for sensitive data on the internet is to make sure only a select few can see it, for now.
(I believe this problem is can actually be solved using something like a Web of Trust (but more formalized/automated than WoT is currently): you'd trust accounts and then you can build a graph where trust is a function of distance (trusted node distance). This web of trust could be useful for a number of distributed protocols. The only catch is it requires much more user interaction and education.)