To call these “fashions” is not to deny that there may be all kinds of social, political, financial, hormonal and psychological explanations for them as well. Nor, Parris insists, is it to trivialise them. Rather, it is to recognise that social pathologies often come in copycat waves which cannot be entirely explained without reference to the movement of the herd. Duelling with pistols became a craze in the late eighteenth and early nineteenth centuries (as you will know if you’ve seen Hamilton or read War and Peace), and not just because of social deprivation or political action. There was a phase fifty years after that when women would regularly faint, or have “hysterics.” Opium was a fashion for a long time in certain circles, just as many kinds of drugs are today. Riots beget more riots, whether they begin for just causes or not. And while it only represents a small part of the picture—and one which is very difficult to tackle directly—the same is true, Parris argues, of many waves of violence:

Grave and dangerous consequences may flow from pursuits that are as subject to fashion as the cut of your trousers. The young are especially susceptible and the young, including children, have an almost limitless potential for savagery. Murder and wounding lie much closer to the surface of civilised man than we like to believe.

Worth considering.