> in the absence of facebook these groups would no doubt still exist.
I don’t think they would.
Creation, discovery, participation, following. None of these is particularly easy if you revert to forums and Google. I won’t join Cute Puppies Forum but I wouldn’t mind following an homonymous group on Facebook for a little while, maybe I’ll answer some questions too.
The average Joe won’t care enough to join their little city group, but Facebook makes it so easy that you find all kinds of non-tech people on it, ready to answer your questions (and sometimes insult you, but I block those on sight).