This is my thought on it, too. I don’t disagree with any of the point OP is making, but I think a larger issue is people misusing ActivityPub platforms and trying to make them into something they’re not. It’s not meant to be a messenger, it’s not meant for privacy. Everything being public and transparent is part of the core design of the Fediverse. The idea of private groups/posts on the Fediverse seems counterintuitive to me.
The “Fediverse” (capital F) refers to the social media platforms utilizing ActivityPub, specifically. I don’t believe there’s any agreed-upon name for such a network on ATProto, since Bluesky is the only platform actively using it.