Re: Worst argument ever
"Not true. Each bill has a unique serial number which can be traced back to where you got it from, be that an ATM, or a bank teller, or a supermarket cash-back or whatever."
Does anyone record the serial numbers of bills that go into ATMs? Where I live, whoever stocks the ATMs with cash can't even be bothered to have all the bills facing the same way.
I would personally think that both currencies are somewhat traceable, but in different ways. Eg, you rob a bank, it's likely the bank has the serial numbers recorded, but money used to do nefarious things is intentionally off the record. With cryptocurrency, while the end result is probably hard to trace, someone had to dump in enough seed money from a bank account, credit card, etc. to generate their BitCoin or whatever, and that is certainly going to be a noticeable red flag.