People in China, at least those millions people who are able to cross the Great Firewall, know that democracy is generally good, but they also know that a strong central government can also be useful for certain circumstances. Most westerners and HongKongers on Hacker news have a very extreme political view, you just believe "democracy is good"(TM), protesting against the evil Chinese government is good. But can you take a closer look at what is really happening in HK and then decide what you believe?
BTW, I'm neither pro-protester nor pro-police, I think the protest is a result of economic regression in HK. You could also check my comment and posting history to see that I'm not a 五毛党.
In a liberal democracy, on the other hand, people expect much more responsiveness to their concerns. And people tend to value freedom of expression and freedom from suppression. Those values are treasured in Hong Kong.
So no wonder mainlanders and HKers have different outlooks on this issue.