Both Hubzilla and (streams), in practice the only Fediverse server apps that have a "public stream" and users other than the dev, can do a lot to keep content private.

But tell that to the Mastodon users who only know Mastodon and the Lemmy users who only know Lemmy, both of whom "know" that nothing in the Fediverse is private because nothing on Lemmy and effectively nothing on Mastodon is private.

[–] scott@hubzilla.monster 1 points 15 hours ago

Does it even matter if they know? The private content is supposed to be invisible to them anyway. The fact that they don't know it exists would make it more invisible.

Also, some platforms, like Mastodon, have actually adopted some privacy. For example, they added "followers only" posts that only their followers can see. If they are aware of Mastodon's "followers only" posts, then they already understand the basic concept of limited distribution.