it wouldn't be too terribly hard to make "cash" less anonymous, for instance, serial number scanners in cash registers - like banks have those safes that are computer controlled and pop out the exact bills and counts you request, just replace all cash registers with either cashless self checkout or those vault style dispensers and receivers. If every point-of-sale has the serial scanner, cash is now no longer anonymous. They'll know who got it, and if someone else gets it scanned then they know that there's a link between you and that person.

there's already enough cameras to capture every angle - including the ones at registers that clearly are there just to capture your face.

The only reason i can see for a cashless society is: someone is going to make shedloads of money on the microtransactions. Visa, MC, AmEx, JP Morgan, etc.

Most of the world already has a "interaction between a natural person and the government is subject to formal identification with government-issued documentation", the US could indeed go that route if they wanted. Nobody could feasibly ban private anonymous communication, though.

That cash will not be anonymous for long once you deposit it, between mandatory reporting and serial number records.