20 years later: Just kidding! Haha!
A lot of Chinese people are touchy when you tell them that part of their country - a part that was taken away from China at the point of a gun in the 1800s - isn't part of China. They're proud that Hong Kong was returned to China, because it's a symbol of China overcoming colonialism, after all the damage and humiliation colonial powers inflicted on China. The Chinese central government is mostly happy to let Hong Kong run itself, as long as they don't try to secede from China, and secession is the primary goal of many of the "pro-democracy" activists.
There isn't really any analogous situation in the United States. Any attempt to make some sort of hypothetical analogy - involving Portland, for example - will sound forced, because the United States doesn't have the same history of foreign powers invading it and carving it up.
In 1997, HKers were afraid their freedoms would erode under Chinese rule. We were left alone for a while, but the spectre was always there. Now, the Central Government has made it more of a priority.
That said, there are many HKers who consider HK part of China and many others who don't.
I'm a Hong Konger and always will be. I'm aware of what the CCP is doing and they're not at all as hands-off as you make them seem. Xi Jin Ping especially does not tolerate differences.
The pressuring of the book sellers to go to China was indeed a very troubling incident. But the general, widespread control of Hong Kong politics by the central government that many people imagine is not there, and almost all of these issues are about the central government not allowing separatists to gain power in Hong Kong (e.g., the entire fight over who can run for the Chief Executive position). Something that is often ignored in these discussions is that under British rule, Hong Kongers has almost no say in their government, and that they now actually have much more say.
True. The foreign powers in the Americas went for genocide and carving it up.
Many mainlanders believe that Hong Kongers are just haughty elites that think that they are higher than the mainlanders.