If we measure the cost of freedom, that simply becomes the level of violence a would-be oppressor needs to promise in order to deny it. There isn't an easy or universal answer here and I'd argue there can't be. To give two historical examples, many Americans raised similar objections against entering WW2 to fight the axis. Some of those same people also opposed the US Japanese concentration camps, for the same reasons.

You might disagree on whether HKers' freedoms are truly being abridged or whether you care, but the questions you posed weren't complete enough on their own.