With Feds showing up with your door with guns and handcuffs, you'll have to hand over your private keys, and that's how they freeze BTC accounts. It's not particularly immune to the same threats.
Yeah, that's the classic xkcd-reality. It will be a rather difficult to enforce that _en masse_. However, should that happen, then the money is the least of one's worries. In any case, financial censorship in that case would be the least of one's worries, if it comes down to such threats and physical violence.
With Feds showing up with your door with guns and handcuffs, you'll have to hand over your private keys, and that's how they freeze BTC accounts. It's not particularly immune to the same threats.