This seems to be related to what came up in another topic about facilitating orientation of community members between open (public) and closed (varying degrees of « private ») spaces, including personal messages.
Dealing with the semi-public nature of the web and semi-overlapping audiences is a major challenge in the online social world. It’s not intuitive. Most communities will grapple with how to make sure people understand how public/private different parts of it are. It might make sense for Discourse to assume this mix of public and private(s) will be the default for most communities and see how it can facilitate navigating it for community members?