Why would the powers that be allow this to happen? I don't understand this fairy tale view
Also, if blockchains prove to be a valuable technology then jurisdictions that ban them will be at a competitive disadvantage.
I make the same argument about self driving cars: yes they could be banned, but SOME government will allow them and then global media will make that difference stark.
You can't hurt the rentiers, e.g. large American banks, and expect them to not get compensation or destroy you in turn. They are the law. To think that it matters that the technology is better (and it's debatable that it really is) is ludicrous.