Well, currently you have to convert cryptocurrency into hard currency to use it, but the former isn't true. I have mined all of my cryptocurrency and that's pretty common among my peers.
Money changed hands for me to get that currency -- money paid to the power company and to a few eBay sellers for video cards -- but nothing requiring an exchange fit-for-purpose.
If purchasing with cryptocurrency ever truly becomes a thing (yeah, I know it exists, but it's rare and becoming more rare these days), that will affect the other side, as well.
It's effectively the only way to do it but the way around it is fairly simple: use a bank account on another country, one that is OK with crypto along with non-US based exchanges.
I wasn't describing that with the intent of laundering money, I mean simply having money in a different jurisdiction and using it locally. I can use my cards from different countries (I've lived in a bunch of different places) pretty much anywhere around the world, the money I have there in those currencies is subject first and foremost to local laws.
Of course it won't stop trade completely, but it could tank the price and cause interest to drop off as that's significantly higher effort than "sign up here, use your credit card or bank account directly".
