Is there any reason for China to trust that the citizens of Hong Kong, long ruled by the British, are loyal to the mainland? Leaders in Beijing clearly don't think so. That’s one reason the political reform plan that they handed to Hong Kong last weekend essentially reserved for the Communist Party the right to vet who will lead the city in 2017.
This was a political decision above all. Yet at the same time, one cannot underestimate the role that outright xenophobia plays in Communist Party thinking. Filled with a sincere fear of creeping Western influence, Chinese leaders see British-influenced Hong Kong as a conduit for outside ideas and separatist sentiment. (It's lost on no one, either, that the city's population swelled in the 1950s and 1960s with anti-Communist refugees from the mainland.) While local pro-democracy activists may have purely domestic considerations in mind, their efforts can look, from this perspective, distinctly anti-national in nature.