First I must say that what's happening to HK is tragic, and I very much empathize with their situation, and am not at all in agreement with how the CCP is handling this.
But this is quite the take! I don't know if you're US-based, but by that logic if the Native Americans held a referendum, they would have most certainly not allowed the U.S. government to form on their land.
This is simply a case of Big Stick Ideology, something the U.S. is quite familiar with [1]
[1] https://en.wikipedia.org/wiki/Big_Stick_ideology
[EDIT: No, I'm not suggesting that this is right, just making an observation]