In a V for Vendetta kind of state, we could. But, fortunately, there are few states like that left on Earth(with Belarus trying to stop being like that right now, but that's another topic). I really believe that in the world we are living, people are getting more and more freedoms, including financial ones, with time, and not the vise versa. Governments have to provide a really strong case for seizing someone's money.
I would not agree that freedoms are actually increasing, especially financial ones were in many countries everything is already under the full control of Big Brother. The whole set of laws introduced by the Americans after the attack 9/11 actually allowed not only the USA to become a totally controlled state, but the pressure from the Americans on other countries is constantly increasing to do the same.
In the case of Bitcoin located on a crypto exchange, the authorities need only express suspicion of the illegality of these funds, and it is up to the client to prove the origin of the property. It is true that rarely will anyone check the history of their coins, so each of us can have some dirty coin because of which the authorities can always ask for seizure.