It is basic crowd control psychology, going back to Le Bon's 19th century work, The Crowd, that annonymity gives members of a crowd a sense that they cannot be held individually responsible for their actions and therefore decreases or removes the deterrent effect of the law and increases the individual crowd member's feeling of power. Identification, whether by tagging or by conspicuous photo/video surveillance, restores the individual's fear that he can be tracked down after the crowd disperses and held responsible for what he has done as part of the crowd.

I only want to see you laughing in the purple rain...