At a university campus demonstration in Bangkok on Aug 10, the images of two men were projected onto a giant screen against a shimmering golden background as protesters mockingly chanted “Long live the king.”

The images were not of King Maha Vajiralongkorn (above), who holds a place of “revered worship” in the Thai Constitution and whose image is omnipresent on city streets, schools and businesses, but of two exiles who have openly criticised the monarchy...