If the government can confiscate gold, what would prevent them from passing the law saying bitcoin ownership is illegal?

Yeah goodluck with that, proving someone has a particular private key. Of course this is all possible but would require the banning of cryptography, and that would take a disciplined dictatorship to pull that off.

The cryptography cat is out of the bag, you can't just ban it(sure you can try, but like I said, good luck enforcing it).

I hope, that US can't return in time of "executive order 6102"

Hauling people away in handcuffs is a much more potent deterrent than randomly shaking people down for a few grand.

It depends on critical mass. If only 2 people are doing it the risk of being the one in handcuffs is a lot larger than when you are 1 of 100 million people doing it.