Message from EunjeeKang
Hi 
I was actually shocked when I first found out about birthright citizenship in other countries because Korea/China(as far as I know)/Japan do not acknowledge it (and I grew up in Korea).
I do not have a great answer for China's case, but I know exactly why Korea does not acknowledge it and I can guess why Japan is the same way.
As many people know, China is a quite diverse nation, and their cultural tolerance is actually much higher than Korea and/or Japan (at least this is how I have felt). However, Korea and Japan are ethnically the most homogeneous nations in the world (Please refer https://www.washingtonpost.com/news/worldviews/wp/2013/05/16/a-revealing-map-of-the-worlds-most-and-least-ethnically-diverse-countries/ ), and the stability of their nation and ethnic identities has been firm for more than 1,000 years old (Japan can be arguable). For example, Korean peninsula's borderline between Korea and China had not been changed a lot since 10th century.
I believe that this stability has assured Koreans and Japanese people that who Korean/Japanese people should be, "purebred".