Advanced persistent threats can exist in any and every one of our computer systems. At any time a government can flip a switch and force us to pay some tax in Bitcoins?
No, they cannot.
And...
Have you been hit by a ransomware before?
Do you know anyone who have been?
Quit being paranoid. Ransomware did exist, still exist, and will exist. With no more power than they had before, provided you have a safe backup of your wallet.
So you're telling me that if each Bitcoin is worth $1 million dollars ransomware or other sophisticated malware and spyware wont be developed to target Bitcoin users? This isn't paranoia it's common sense. Governments may or may not have hit any of us already with advanced persistent threats. Do you think they'll tell us?