For the Chinese leadership, the former Portuguese enclave of Macau is now the model post-colonial child: dutiful, attentive and obedient to parental dictates emanating from the north. By contrast, neighboring Hong Kong, a British possession for more than 150 years before its 1997 handover to Chinese rule, has turned out to be Beijing’s enfant terrible: querulous, petulant and defiant in response to Beijing’s paternalism. On July 1, Hong Kong will mark 20 years since the Union Jack was lowered and...