I would think that the distinction lies in the time it takes to reach consensus. An individual person's moral values may change rapidly without the need for external validation. A book club may take a few weeks of debate over a heavily philosophical book to modify the perceived moral values of the group as a whole. But stretching large moral shifts across an entire populace would probably take more time and a more concerted effort to accomplish. New ideas or values need time to be sorted, whether they be picked up into the mainstream view or dropped into unfavourability.