Before Saudi Crown Prince Mohammed bin Salman arrived in Beijing for a major visit late last month, he was the target of an intense lobbying effort at home and abroad. Members of the Uighur diaspora in Saudi Arabia and beyond hoped the young, powerful royal would acknowledge China’s nationwide crackdown on its own Muslim population. For the past year, a state-sponsored campaign against expressions of Islamic piety has roiled Muslim communities throughout China—especially in the northwestern region of Xinjiang, where analysts now estimate that more than 1 million ethnic Uighurs have been detained in so-called “re-education camps.”

Instead, as he was greeted warmly in Beijing, the crown prince affirmed his support for the Chinese crackdown. According to China’s Xinhua News Agency, he told Chinese President Xi Jinping that Saudi Arabia respects “China’s rights to take counterterrorism and de-extremism measures to safeguard national security.” Although MBS, as the prince is known, did not specifically mention Xinjiang or the Uighur minority, his statement parroted the vocabulary Chinese officials have been using to justify their program of mass detention. ...