It’s on the internet. Public. Got it. It’s almost as if, and hold on to your hats here, the whole point of posting on something like Mastodon or Lemmy or so is to have a public discourse, as you cannot know who will be replying anyways. It’s almost as if, and this is getting wild, I know, read-access being public is intentional and explicitly part of the design.

This is true for Mastodon and Lemmy and I generally agree with this sentiment.

That said, ActivityPub is more than just Lemmy and Mastodon. ActivityPub is more general than that. Lemmy and Mastodon are designed in a way where public discourse is the default and everything you write is expected to be public. But ActivityPub on its own has no such assumptions. There's nothing about ActivityPub that says that you cannot build a more private social media with it. But actually you can't really, because of the problems that the blog post points out. But the vision I think for some people is that this should be possible.

I'm personally not 100% convinced that that vision is even possible though tbh.