If we officially opened our borders today, what makes you think we would not have millions of Chinese pouring in as a result?
How many could we absorb without changing our culture unrecognizeably? 10,000,000? 100,000,000?
Eventually we might even be economically better off, but we would also be more crowded, and our children would have to learn Mandarin just to get a decent job.
I suppose we are fortunate to share borders with 90,000,000 Mexicans and 33,000,000 Canadians than with 1,200,000,000 Chinese. Luckily, the Pacific is too far to swim across.
There is such a thing as to much of anything, and that includes good things.