WSC, I'm not sure Flickr is a great example. The restricted images policies only work because they employ a full time set of "police officers" with the massively unpopular duty to delete images and close accounts (including those that have paid in advance for their "pro" account) using their own personal judgement using a classification system that has no clear definition, independent appeal or assessment process.
WMF *could* force Commons to become such a policed service (perhaps by paying admins a salary; yea where can I sign up?) but we would probably not consider it part of an open community from that point on.
Cheers, Fae