The reason civil authorities should never allow riots to swell is because of the social nature of human beings. On their own, very few people freely assault strangers on the street (thank God). In a social frenzy, however ... (1)

herd instinct kicks in. The willpower an individual might have on his own is slowly surrendered to the group. If the group spirit bends toward violence, its individual members bend toward violence. After a few hours, or days, or--heaven help us--weeks of this, individuals ... (2)

*find themselves doing things* they would never do on their own (or at least that's how they perceive it later). So an activist for racial equality will cheer the murder of a political opponent in the street, and the high-minded crowd will *cheer her on.* (3) ...

Competent civilian authorities understand this, and arrest the first guy who throws a brick through the first Starbucks window, and the second, and the third. If they fail to do this, they are tacitly encouraging the herd instinct of violence that will inevitably follow, and (4)

in effect invite a more draconian crackdown later from a larger jurisdictional authority, or worse.