The example you're referencing was mentioned in the article, and I think is part of the reason Haidt took the time to prove that this phenomenon is _not_ isolated to the US, and that US specific issues (like school shootings) are unlikely to have an effect elsewhere.

> And it certainly can’t be caused by the most popular theory we hear in the USA: school shootings and other stress-inducing events. Why would school shootings or active shooter drills implemented only in the USA lead to an immediate epidemic across the entire English-speaking world?