I agree with you. But I don't believe that's relevant in this situation. This isn't about exporting democracy to China -- it's about preservation of Hong Kong's way of life. The only culture that's being imposed here is by the Chinese government on Hong Kong.
Again, all of these things happened long before any of the parties involved were ever born. Who does this affect more? Hong Kong changing their way of life, or China thinking that something belongs to them? Which one will impact individuals lives more on a day to day basis? Think about what you're saying. China not being able to lay claim to Hong Kong affects the average Chinese person how much? China laying claim to Hong Kong affects the average HKer how much? I can tell you that the answer to one of those questions is much larger than the other. If we were to take this template and apply it elsewhere, does the template hold up and make sense? Let's say slavery. Sure, you could find some upset descendants of white plantation owners who feel that it was unjust that their 'property' was taken from them, and emphasize some heavy nuance on how we don't understand how complicated things are and how descendants of plantation owners have some legitimate gripe. So? Perhaps that's too extreme. How about the revolutionary war? Lots of British thought the colonies were theirs. So? Should the US revert back to England, way after the fact, because they believe it was ultimately theirs, that started colonization, and that the rebellion was unjust? Does any of that history mean **** to people today?
Should Hong Kong lay down their way of life because nearly 200 years ago "this belonged to China for a really long time"? Ok. Some land was part of the Chinese empire. How about the people -- alive now -- who weren't way back when this happened? What about them?
