‘You should not sleep at night!’ a student screamed at Yale professor Nicholas Christakis in 2015. ‘You are disgusting!’ Students surrounded him, yelling obscenities and threatening him while he tried in vain to reason with them. The abuse stemmed from the fact that Christakis’s wife, Erika, had questioned whether it was Yale’s business to email students on Halloween instructing them not to dress in costumes that might be deemed ‘culturally unaware or insensitive’. The video of the mob went viral, exposing a wider audience to a strain of radical cultural intolerance that has been pulsating with increasing ferocity on university campuses since the early 2010s. A new lexicon of terms – ‘trigger warning’, ‘microaggression’, ‘safe space’ – has entered the American vocabulary. Alongside open letters denouncing deviant academics, events or speakers (I recently had the experience of being targeted), social media has been used to destroy reputations, cause professors to lose their jobs and prompt journal articles to be retracted.