When a Hong Kong Legislative Council meeting ended in a brawl a week ago Saturday with one lawmaker hospitalized, the Hong Kong government denounced the ”unprecedented” fight. But what did it expect? The weekend scuffle concerned a proposed extradition law that would allow the transfer of local residents from Hong Kong to Mainland China and eviscerate Hong Kong’s legal independence.

In the 1997 handover from British to Chinese rule, Beijing promised Hong Kong a high degree of autonomy under “one country, two systems” until...