The US can control the exchanges on the US, also they will probably ask for proof of transactions if you want to cash out. And if you bought a token/coin that's against US regulations being a US citizen you could probably have problems too.
Thing is a big part of crypto is trading, and going from fiat to crypto and crypto to fiat, and they can definitely control that.
A government is always conservative and it wouldn't want to change the way it runs. This has been seen in the history.
A mass moment is what needs to make government fall in line with the demand of time. The government needs some pressure to make a change, not necessarily a protest. Facebook's announcement of Libra is an effective start of the mass moment.