That is exactly as dumb as trying to make the internet illegal. It would financially ruin any country who tried it and give a significant advantage to everyone else on the planet.
....That is an extraordinary claim, and thus requires extraordinary evidence.
There is no significant legitimate commerce taking place using cryptocurrency. By what mechanism would banning converting BTC to USD "financially ruin" the US?
It would certainly be bad for ransomware companies, who probably make up a substantial portion of GDP in some dark corner of the world. Think of their children!
