Every individual has his own characteristics. Some Chinese people are articulate and charming, they no doubt promote. Others are not so much. They probably have a negative effect, if anything. Take an example, Chinese counter-protests against Olympic torch protests or Tibet protests, and let's see if a local western find that a particularly fine promotion of Chinese culture, values and interests.
I am not sure how you can possibly assume that just because a Chinese person brings some aspect of China with them they would automatically promote anything. Give you another example. Mid to late 19th century Chinese immigrants to America were a very hard working people. Some of the ideas they bring to the Western mind about China is the stereotypical pig-tailed, dirty, scrapping, dog-eating 'Chinaman'. Still think all overseas Chinese promote Chinese culture just by interacting?
And oddly enough, you can actually celebrate a sporting event without actually supporting the country. And San Francisco, believe it or not, is an insignficant part of the persons of Chinese ancestry as a whole. I fail to see how you can generalise a bit of real estate with Chinese signage and people turning out on parades does not actually make them Chinese? I am sure they turn out in force to celebrate Christmas, too, does that make them all Christians? At its highest it makes them Chinese-Americans. It does not make them Chinese, and therein lies a big difference..
You fail to understand that people are complex animals. They can hold somewhat different and maybe contradictory ideas in their heads, like 'I am Canadian' and 'I am Chinese' to form their own unique identity. So they can go on a Chinese New Year parade one day and then happily go to Canada Day celebration the next (well, not literally the next day). It's when the chips are down and it comes down to a choice between, say, China and their adoptive homeland - or that of their own - interests that one can determine their loyalty. I want you to look me in the eye and tell me that an 'average person of Chinese ancestry' will put Chinese interests first.
And guess what, assimilating a conqueror is hardly an exclusively Chinese phenomenon. Quite a few peoples did it. Norse and Huns disappeared into Christian European, Rusyn' adopted Greek Orthodoxy and script, the Turks saw themselves and successors of Rome, Persia swallowed up her Arab conquerors, and India ate up more conquerors than you can count. The fact that you actually think this is a unique phenomenon speaks volumes about your skewed view, and even blinder to the fact that assimilation goes both ways. There is a lot of 'barbarian' blood in Chinese culture, starting from the semi-'barbaric' Qin and Chu kingdoms through the volkwanderung of the 4th to 6th centuries, the Tang dynasty, and so on. China's 'identity' CHANGED. You can blindly close your eyes and claim that China retain the same national identity over the last 2 millennia of a sometimes-united Chinese state, but that is equally ignorant, if not more so.
There are plenty of other peoples who endured similar or worse and retained a similar sense of national identity over a similar period. The Jews, the Persians, the Greeks, the Romans, even the Turks have an astonishingly robust national consciousness stretching over 1300 years.
China is not unique or special, get over it.
Hogwash. I donated 5,000 HKD to Sichuan, are you saying I am Chinese now? Having sympathies due to common cultural heritage is not the same as identifying oneself as Chinese. JAPAN and KOREA gave large amounts of donation, and so did the largely hostile Taiwan. Are they Chinese too?
So what do you serve if a conflict boils over over Taiwan? It's not always Chinese cultural evenings and Chinatown new year parades, you know. When the conflicts are below the surface, it's easy. Try looking at times when things are tough.
Why don't you consider the nation of Singapore? An entire nation of OVerseas Chinese, do they always act for China's best interests?
The crux of the matter is that you made an extremely bold claim that overseas Chinese are out there to promote Chinese interests, I have yet to see a single piece of actual evidence backing this up. Chinese emigrants are people just like any other sort of emigrants, they emigrate for their own personal reasons, they do not go out there for the good of China as a general rule. Back up your assertions with evidence and reasoning, retract it.