Countries who have successfully gained independence have often sacrificed a lot of blood for it. And built strong armed forces to back that independence up with.
Whatever we may think is morally right, HK does not seem to be putting together that hard resistance, nor is it building up its own armed forces to declare and maintain independence with. China thinks HK is legally theirs and nothing we say or do will change their position over it.
That's why I don't see these protests achieving anything.
Note that there has historically been another way, to force the oppressor to be brutal enough that they, or the people sent to do it, will turn on the government. This worked in India against the British and almost worked in Tiananmen, rural army units had to be called in. I don't think it will work currently against China, but it is the only thing HK protestors are willing to do which I respect them for.
Whatever we may think is morally right, HK does not seem to be putting together that hard resistance, nor is it building up its own armed forces to declare and maintain independence with. China thinks HK is legally theirs and nothing we say or do will change their position over it.
That's why I don't see these protests achieving anything.