I get what you are saying but someone with millions to launder would have to set up probably multiple cash flow businesses in order to clean it, if they try to just buy things little by little it gives more tume for the cash to make it into a ledger and gives more opportunities for the government to catch on to the transactions. There is already advancements in bitcoins privacy like silent payments. Not a silver bullet but there are other tools like coinjoins and if the person knows what they are doing they might be able to use ecash. Development hasn’t stopped and all this can be done right from the computer. So i actually don’t agree that cash is more fungible.