Perhaps part of the reason for our difference of opinion has to with communities vs. sites vs. instances. In my understanding, Communities are part of a single Instance of Codidact. In some ways that makes them no different from multiple Chat Rooms in chat system or multiple Topic Categories in a forum. Yes, there will be some positive action required to say “I want to be a part of Writing” vs. “I want to be a part of Worldbuilding” etc. But in reality you start by saying “I want to be a part of Writing” and the system responds with “OK, set up an account (email, confirmation, blah blah blah” and now you are part of the Codidact system and have privileges of “Trust Level 0 on Writing” and “read only, just like the people who haven’t registered, for everything else”. Then you post some Q&A, build up to Trust Level 2 and then say “I want to join Worldbuilding”. The system says “OK, you’re already a member of Codidact so let’s see: You have TL2, so we’ll get you in to Worldbuilding starting at TL1”. It is all one system. So one database, one set of credentials, etc.