Merchants interested in hiding their activities might do this. However, legitimate businesses probably would not. If you are a bank and the FBI shows up at your door, you could offer them a copious supply of logs, or you could tell them that you do not keep records.
Legitimate businesses are concerned about the privacy and security of their customers. Banks are required to keep certain records, but other businesses only need to keep the records required for accounting.
As long as the business keeps the lawful minimum records, the FBI cannot shut down their legal business, without a court order. They can record cash amounts, without necessarily recording any Bitcoin IDs or IP addresses.
In the real world, there are plenty of places you can pay cash, and the date, time, amount of cash you paid and the thing you bought is the only record they'll keep.
What do you think happens when Bitcoin payment terminals start appearing at stores?
You don't care which ones are real - you just care about every account that the money touched. You then monitor them all until you link one to an account you know the owner of, and then you can start tracing backwards in the real world.
If every bitcoin user is generating a new Bitcoin ID to receive every spend, then the money never touches a "known" ID; since every ID it arrives at is "brand new".
It's very possible the BTC could be used to obtain virtual goods or online services, without a "real world known ID" ever involved.
The virtual goods or online services might be received, without the merchant ever gathering and keeping any details about the buyer.
The virtual goods or online services might be convertible to real cash indirectly; for example.... use BTC to buy Facebook/Twitter followers, other methods of using BTC indirectly to get cash by generating business, instead of selling BTC for cash.
There may be complicated arrangements there certain people are paid for the virtual service of receiving a virtual good, or paid a commission to act as a sender or to act as a receiver in a "blind handoff".
There are plenty of ways of disposing BTC, which do not necessarily provide a path that could be reversed from real-life
Presumably: the illicit user will buy all services using BTC, and only buy products/services that are virtual, that they can get without revealing their identity to the seller.