On Hubzilla, there is a way to make the public stream available and only show posts from that server. But most Hubzilla admins never turn it on and probably don’t know it exists.
As an administrator, the only time you would want to turn on the public stream is if you are a public hub and accept new signups. It makes it easier for administrators and moderators to moderate the public content on their own server since they can see all public posts in one place. If someone is posting illegal content or spam, a moderator can see it, and remove it (and perhaps the user too).
But private instances don’t need this since everyone on the server is trusted.
@Jupiter Rowland
That’s true. We are protected by Section 230 of the Communications Decency Act and the Digit Millennium Copyright Act (DMCA) and the common law legal concept that you cannot be held liable for someone else’s actions.
Other countries may not provide the same protections.