> There are plenty of large groups that people derive social value from, maybe even most.

I'm not sure what you mean here. Do you mean groups on facebook or that there are other groups on the scale of facebook people (ie. a user count in the billions) derive value from?

For the first, in the absence of facebook these groups would no doubt still exist. There were forums before facebook and some of them grew quite large. There were even regional social networks on smaller scales (I worked for one once).

If you mean the latter, well, I don't think that's really true. In so far as it is, there are only really a couple that aren't just owned by facebook to begin with.