Seems like this could be fixed fairly easily with a set of gatekeeper options. When a group gets created, you could have the option of making the group Public (

Seems like this could be fixed fairly easily with a set of gatekeeper options. When a group gets created, you could have the option of making the group Public (anyone can join), Invite-Only (anyone can join with an invitation from someone already in the group), or Vetted (requires an invitation to join and the person who made the group must approve each person who tries to join). That way, you account for varying levels of paranoia.