There was a time when the human species was small in population and faced attack from predatory animals.
Evolution then favored those who possesed genes that fostered the Herd / Mob instinct.
The weak and isolated apes would gather into a frenzied mob and hurl stones at the attacking carnivore.
Had each primate engaged in rational thought about danger to the self, the mob would have never formed. Evolution found a way to reward those whose genes allowed mob mentality to override rational thought.
That was then. This is now.
We see in the picture to the right, a mob of humans attacking Egyptian police officials because a ferry sank and loved ones were lost in February 2006. The mob attack will not bring the loved ones back. The mob attack will not drive away predatory carnivores.
And yet it is there. Deeply etched into the makeup of the human critters.
Genes that once worked to preserve the species now drive it over the edge.