The loss of a common enemy and those other trends with roots in the 20th century can help explain America’s ever nastier cross-party relationships, but they can’t explain why so many college students and professors suddenly began to express more fear, and engage in more self-censorship, around 2015. These mostly left-leaning people weren’t worried about the “other side”; they were afraid of a small number of students who were further to the left, and who enthusiastically hunted for verbal transgressions and used social media to publicly shame offenders.

A few years later, that same fearful dynamic spread to newsrooms, companies, nonprofit organizations, and many other parts of society. The culture war had been running for two or three decades by then, but it changed in the mid-2010s when ordinary people with little to no public profile suddenly became the targets of social-media mobs. Consider the famous 2013 case of Justine Sacco, who tweeted an insensitive joke about her trip to South Africa just before boarding her flight in London and became an international villain by the time she landed in Cape Town. She was fired the next day. Or consider the the far right’s penchant for using social media to publicize the names and photographs of largely unknown local election officials, health officials, and school-board members who refuse to bow to political pressure, and who are then subjected to waves of vitriol, including threats of violence to themselves and their children, simply for doing their jobs. These phenomena, now common to the culture, could not have happened before the advent of hyper-viral social media in 2009.

This fear of getting shamed, reported, doxxed, fired, or physically attacked is responsible for the self-censorship and silencing of dissent that were the main focus of my essay. When dissent within any group or institution is stifled, the group will become less perceptive, nimble, and effective over time.