That's not fungibility, that's just an association issue. If someone denies doing business with you because you bought (or sold) a Trump hat, that doesn't make cash non-fungible.
(Incidentally, banknotes all have unique serial numbers and can be traced to criminal transactions by either the serial or by more mundane taints/markings)
Fungibility accurately describes the main problem here, right now some bitcoins are worth significantly less than others because they’re tied to hacks and you can’t send them to any normal exchange without immediately getting your account frozen.
You will have to spend more than 1 “dirty” bitcoin to get 1 “clean” bitcoin. Almost nobody will accept the dirty bitcoin, whereas basically everyone will accept a bank note no matter the history of said bank note (cops might show up at your door later, yeah).
But sure, eliminating traceability inherently solves this issue too.
If you want to buy something and the guy says "I'd love to sell that to you, but your $100 was stolen in a bank robbery two years ago and it's on a list with its serial number"... well, that $100 isn't fungible, is it? Has little to do with the association, it's not you, it's the money itself. That said, my example is one that proves this happens for cash too. Extreme corner cases are funny like that.
(Incidentally, banknotes all have unique serial numbers and can be traced to criminal transactions by either the serial or by more mundane taints/markings)