Usability Yes. Social Features, Uh-Oh.

I don't know that it has to be "invite only". Just that we want to keep track of who is doing the inviting, and if there is a pattern to the editors they are recruiting. A wide recruitment of active editors is good. But a systematic recruitment of editors who all share a specific POV would give the group undue weight.

But the creation of a group in the first place should definitely have some kind of approval process. And a recall process, too, for extreme cases.