As for your idea that they could just kill all Bitcoiners...
That very much depends on where you are and who it is that might be coming for you. I think most of us already know if we live in a place where a gang might roll through and round us all up.
If they're not rounding up whole neighborhoods, if they're actually trying to identify Bitcoin wealth and bury it, prevent it from being used, they will have a very hard time.
A Bitcoin wallet can be accessed by multiple people across the globe from one another. Kill one, there's a backup key and person too. It doesn't work as game-theory to fix Bitcoin undermining the fiat printer. Its is very difficult to prevent Bitcoin slipping through your fingers if you squeeze it. This lack of friction is why it's better than gold shipments as payments, even though gold is more private and just as scarce for now.
China banned Bitcoin and they're not shy about forcing their citizens to behave a certain way. They would like to ban holding Bitcoin, I'm sure. It's not feasible to enforce it, and doing so without enforcement would betray their weakness in this regard.
If your local government is just performing a genocide, then Bitcoin and privacy is irrelevant.