I've wanted to write my thoughts on this for a while. I hope they are working to solve this problem, but in short I feel too much emphasis has been put on allowing users to limit who sees their posts, instead of focusing on creating engaging supportive dialog to posts through smaller groups.
I'd be interested to see what solutions others have for this problem, but who hasn't read a comment on Facebook before and went to comment only to realize the group was too large to write that inside joke?