Whilst I'm not a big (or even regular) social group user, nor do I expect my opinions to be taken as gospel, I would be remiss if I didn't at least register one particular concern that springs to mind regarding this new endeavour. Specifically:
Perhaps it would be better to just give all new groups the option of applying for private status when requesting approval, which would be granted if sufficient reason was given (such as would be found, I'm sure, for the above), or something along these lines? Still, even if that approach proves to be unmanageable for the staff, I don't think banning private groups altogether is the right way to go either.
I apologise in advance if this has already been discussed (though I can't see that it has, at least in this capacity), but I feel like this issue needs to be raised.