Because the people of China have no choice but to listen to whatever the government wants? Tell the government to allow people to vote first then I will vote. Gee get real. Also, please don't play smart with me, I have never said China should secede its current territory.
It's the people that matters, not land. If we Chinese living outside can contribute to China, I am pretty sure we are more valuable than some barren piece of land. Also, do repeat to yourself over and over, China's border has shifted numerous times in history, but it came back again because people share the same culture and have the desire to unite. Not by force, but by cultural identity. If a land is occupied by too different people, they will eventually break off.
Blind expansionism never lasts in history, and will never last in future. The Mongols and the British are good examples.