Almost 19th Century in its pig-headedness, the only way it makes sense was a propaganda act for internal consumption - but with exceptionally destabilizing effects outside their borders.
The only positive aspect of their act, at least from the American point of view, is that it will drive Japan, South Korea, The Philippines, Vietnam and others closer in to our orbit as they start to recognize China's ambitions for what they are.
The bad part of that, is we need to be mindful that those who are closer to us are not under our control. Humans are imperfect institutions and things can get out of control.
South Korea isn't really being helpful here;
South Korea is finalizing plans to expand its Air Defense Identification Zone (ADIZ) in response to China establishing the East China Sea ADIZ, local newspapers are reporting.History; she is such a needful and insecure woman. She will not be ignored.
According to a number of local reports, ROK National Security Office chief Kim Jang-soo convened a meeting of top South Korean security officials on Sunday to discuss the new ADIZ.
The Korean Herald reported that the ADIZ is rumored to include the “country’s southernmost island of Marado; Hongdo Island, an uninhabited island south of Geojedo Island; and Ieodo, a submerged rock within the overlapping exclusive economic zones of South Korea and China.”
Yonhap News Agency quoted an unnamed local official as saying “(The new KADIZ) has been conceptually finalized. The government will announce the plan after carefully reviewing the military operation and aviation safety as well as the international regulations.”