The facebook group is no basis to go on. You just add whomever you wish you don't even need their permission. Same as our group on facebook.
Just seen someone add 45 other members (without their permission ) and by one click of the mouse, onto the Nextgenus facebook site.
Not just a Nextgenus issue, I imagine that a lot of Facebook sites pump up their "members" through dodgy means.
I have previously been added to facebook sites ( most that I have never heard of ! ) by "friend of a friend of a friend" etc
Absolutely scandalous that the site owners allow that to happen....assuming of course that facebook allows them to stop it.