South Korean missile defence has prompted a middle-class boycott from Beijing

“Chinese tourists are the [country’s] army,” one commentator on a television talk show recently quipped—and he wasn’t far wrong. The discussion was about how South Korea had fallen out of favour with Chinese travellers. Last year, it was the top international destination for the week-long May holidays; 12 months on, it had slid to tenth place.

The big plunge is because of South Korea’s embrace of THAAD (Terminal High Altitude Area Defence). Developed by the United States, it is a land-based system of…