Hong Kong residents who may run afoul of the Chinese authorities already feel vulnerable. In 2015, five staff members of a Hong Kong bookstore and publisher disappeared into the Chinese legal system. Just the threat of extradition on trumped-up charges would be enough to stifle democratic actions in Hong Kong. A week ago, for example, thousands of Hong Kong residents held a vigil to commemorate the 30th anniversary of China’s Tiananmen Square massacre. No such protests are permitted on the mainland, of course.