Chances are that if you don’t look Chinese and engage in any activities critical of the Chinese government or its many affiliates you will at some point be accused of being a foreign spy. If you are an actual spy, which includes anybody working for an organization at least partially funded or endorsed by a foreign government, you will be accused of ‘meddling with China’s internal affairs’, which we can only guess is some kind of treason.

The logic becomes particularly twisted if you are a Hong Konger by birth and/or have lived here for your entire life. Hong Kong media often at least partially buys into the idea by using terms as “foreigner” or “expat” as descriptions of race rather than what they should be: descriptions for residency or employment arrangements.
China’s national identity is built around ethnic labels, with various sometimes hardly distinguishable ethnicities given the status of ‘nationalities’. No effort has been done to change the Chinese identity into one of statehood and (passport)-nationality, even though this would make it far easier for the state to integrate and accommodate ethnicities and language groups that do not feel part of the ‘Mandarin Han” clique.
Given all the other ancient Chinese ideas that the Communists tried to overthrow during their now 65 year rule, how is it that racial self-conception was not just being left out, but even further codified and perpetuated? A tribute to Tito’s Yugoslavia?

Hong Kong’s cosmopolitan mix of ideas, languages and people does not only make Beijing uncomfortable because of the liberal (in a political science sense) mindset it creates among the citizens, but also because it creates an environment in which Hong Kong is no longer clearly a Chinese city. Beijing is terrified at the idea of the 300,000 mostly Indonesian and Filipino women becoming permanent residents, giving birth to statistically 420,000 non-Han children. Beijing also feels uncomfortable with a significant number of other foreigners calling Hong Kong their home, possibly acquiring Chinese citizenship or, Confucius forbid (actually he wouldn’t!), any meaningful voting rights.

Together come two ideas that are so deeply rooted within the establishment of China (and many other countries), it is quite likely the officials honestly and wholeheartedly believe in it:
1) Nationality is linked to ethnicity. If you don’t look Chinese, you can’t really be Chinese (and your passport is lying or acquired through dubious means).
2) Individuals do not have their own opinion. They represent the interests of the organizations that they work for, or whose plastic cards they hold.

Point 1) is perpetuated by many more people than we think. This is not only because we often cannot distinguish if someone is referring to a person’s nationality or their ethnicity, but also because ethnic identity is often very important for Chinese people. “American born Chinese” is used by everyone, but it comes predominantly from Chinese emigrants who amplify their ethnic identity when talking about themselves in front of their children. Few other cultures do this, and I’m not aware of any that do it to this extent.
Even less reactionary news outlets such an Inmedia or Apple Daily repeatedly refer to any non-Chinese as foreigners, despite many of them being as well as established as those characterized as Hong Kongers.

Point 2) is the politically far more important part. It is very much possible that officials inside the Chinese government actually believe that they not only accurately represent their country’s opinion and interests, but that every official of any government accurately represents their country’s opinion. People who deviate from their government’s opinion must then in conclusion represent another government’s opinion.
The only possible link then would be that this person is a spy or an agent or bribed by this foreign government, and the only reason they would do that is because they want to undermine social harmony and national security and whatever.

Many foreigners are afraid to join protests or voice their support for social movements such as Occupy Central or the Student Strike because they do not want to be accused of being a spy, but also because they fear that the presence of Caucasian or Indian or Arab Hong Kongers could damage the reputation of these movements.
What they do not see is that in the eyes of those that accuse anyone of being a spy for voicing an opinion, anyone in the protest is already a spy, no matter what their eyes look like. These people are so convinced that they represent public opinion that anything challenging them must be an elaborate plot by at least their political opponents, if not their national enemies.

That is why showing your presence is the only thing that has any chance of getting these people to back down from their stance. Even if it’s unlikely to convince them, it is very likely to convince the people around them that public opinion is against them.
Political leaders do not step down because they see that they made a mistake, they step down because their advisers, aides and employees urge them to or silently drop their support.

Individuals have opinions, and they need to voice them, or else someone will assume you are part of their silent majority.