Actually on the black market the US is known for money laundering, funding terrorism, and lots of other illegal activity. The black market is cash based after all.
It's a simple test. Pull out a dollar or euro or whatever out of your pocket. Are you thinking about the groceries, rent, food etc. it can buy?
Or how many times it's been used in funding terrorism, money laundering and other illegal activity? If the answer is the food, rent etc. the fiat is probably more famous than infamous.
Sure I must have, but for many years now most people use debit and credit cards for legal purchases. It helps you avoid having change. Cash is for drug dealers.
The state agrees with you. Which is why China is insisting on cashless payments to have complete surveillance over the transactional activity in the country.
We don't even hae to have anyone insist on it. We just prefer it. I hated having all the loose change. I use to throw out any coins less than a quarter.