This may seem nitpicky to point out that it does, but since it does, I'm not sure of your point.
"A unique combination of eleven numbers and letters appears twice on the front of the note. Each note has a unique serial number"
https://www.uscurrency.gov/denominations/bank-note-identifie...
moreover we are assuming that cash is ID at entry and exit, which its not, unless someone suspects something.
So when a cash machine gives you money, the ID of the currency not be tied to your account. When you spend that money in a shop, those notes will not be attached as having come from you as a customer.
With bitcoin, that all comes for free, we know when money left your wallet, what addresses it passed through to get to someone's else's. the whole selling point of bitcoin is that you can trace the provenance of each transaction right back to when that coin was originally mined.
For example, if I was to use bitcoin as a bank account replacement, everyone would know my employer, they would know how much money I give to my spouse each month. They would know who I invest with. They would know when I do my shopping at the super market. They would know when I'm having work done at the house. They would know if I got a bonus, and how much.
Some of those things I'm ok with, but a lot of things, I'm not
If you mean physical units of currency that is no longer the case, most notes have serial numbers. In principle quite a lot of tracing can be done.
there is lots of scope for laundering by giving the cash to third parties, before it gets to the banks.
Laundering inside bitcoin is pretty futile, because we can trace from mining to current wallet. we don't even need to trace all bitcoins.
All you have to do is pay for something illicit, and you can trace the flow of money from wallet to wallet, until its either converted into real cash, or held as a "reserve"
Outside of some exchange link keeping a name = address record, the public wallet doesn't really expose you as there's no link between an address and a person.
Also, that $1 can be charged with crime and sized directly. Good luck siezing a brainwallet etc.
Edit: like IP address and torrent lawsuits etc.
its really not.
unlike cash or bearer bonds, _all_ transactions are recorded in perpetuity. That's literally the entire selling point of bitcoin, the ledger is opensource and universal.
Given that virtually all money going into and coming out of bitcoin is through establishments that have financial licenses, its perfectly trivial to trace the flow of money from its first exchange of real cash for bitcoin, to when its used for illicit purposes.
You're currently labouring under the impression that tracing cash flows in the real world is hard. its not, especially for a government. what is hard is proving that its illicit. cash is fungible, as in each unit of currency has no ID. so its much harder to prove that this $1 came from a drug sale.
with bitcoin, you have a public wallet, and a clear lineage of transactions from start to end.