They are exploiting the system and considering the kids grew up in China, their allegiance is likely to be with China , for a good many of them. There have been countless cases of spying and industrial espionage by Chinese students or residents. China is a very Nationalistic society, so the odds a fair number of these birthright children's loyalty is to their motherland is very high.
When the 14th was written , no one envsioned hundreds of thousands of Chinese and other Nationalities flying into the US to give birth and claim citizenship. The 14th was meant to free the children of slaves, not allow people to abuse it like they do now. The spirit and intention of the law is being exploited and abused. People who emmigrate here the legal way have to wait for years and meet certain qualifications, but these birthright abusers just fly in and claim citizenship for their kids.