My admittedly nascent theory is that, in spite of the anger, most people actually feel embarrassed or ashamed by the violence/inhumanity/ambush.
Are you seeing this in other images, at least at the point of a one-on-one attack? What do you think of the theory, and what are you seeing in the way of other examples? Perhaps you might post an image to verify or contradict the effect.
(image : Bradley C. Bower/Associated Press. caption: In one angry confrontation, Craig Anthony Miller, standing two feet from Senator Specter, shouted into his face during a Town Hall meeting Tuesday , Aug. 11, 2009 in Lebanon, Pa.)