1. It was very good of proposing an all-purpose document so that people can use it anywhere, anytime, whenever, etc.. Now we can't.
2. Hu Kou is Hu Kou, Liang You Zheng is Liang You Zheng. Every document has its own usage. A birth certificate is the evidence of a person's birth geographic information to proof his immigration status(not from any dictionary). A travel document is to allow people to travel to other countries with permits (not from any dictionary as well).
3. What are the reasons not to use an international wide document?
4. Why to give the immigration officers a harder time to recognize the documents statistically rare to appear?
5. Let suppose such a case. A canadian birth certificate is easily recognized by any canadian authorities. But, when a people holds such a document goes to Viename, Thailand, or South Afarica, do people there recognize such a document? It is easy to leave/reenter Canada, what about the countries to be visited?