The bank doesn't scan the serial numbers on the money I deposit and yet they somehow correctly credit my account.
Well not _you_ but bills do get flagged if they're involved in crimes (like kidnapping or robbery). So when they're deposited in a bank the FBI can track the _relative_ location of criminals.
I think it would be good to have an optional KYC/AML attached to cryptocurrency transactions. In this way they can be more popular and more connected to the regulated world.
This is already the case, minus the optional part [1]. Broadly, I'd guess anyone involved with an unregulated money transmission operation is one pissed-off D.A. away from serious jail time.
[1] http://www.coindesk.com/bitcoin-law-what-us-businesses-need-...