The host is the person who enforces whatever rules there may be, and will therefore be seen by many as a species of law enforcement officer. A host is also an exemplar. A host is also a cybrarian. Well performed voluntary cybrarianship is contagious. A host can be a character in the show, but the show is collaborative improvisation, with the audience onstage.
All hosts are members of a community of hosts.
You can't host communities without communities of hosts. They are gardened. All online systems tend to fail to cohere without careful intervention. All online social systems are challenged by human social foibles and technological bugs that tend to split groups apart. Positive effort is required to create the conditions and garden the growth of a self-sustaining group.