I have lived in U.S. for a few years and I think this county is more just, fair and decent than a lot of other countries. But just thirty years ago, a white American could well feel sad for the socail injustice this country had done to black people. But the same person should feel much better today than thirty years ago.
Who made the difference? Not the U.S. government, not Martin Luther King Jr., not any other single institution. It started with the personal effort of those few people who hated the social injustice, and then it evolved into the majority. Had the first few people, touched by the sadness, thought they could not change anything when the task seemed so immense, the social justice that american people enjoy today would have never came.
The same logic applies to China today. Making China better starts with you, me, and everyone around us. If we walk away, nothing will change thirty years from now.