And no, things like monero and zcash aren't a working solution to this problem either, that's a whole different discussion though.
Things like the Bank Secrecy Act are only there to guarantee a level of secrecy/protection from other customers. Law enforcement, government, and third party service providers are not counted there realistically. If you want financial privacy, you keep your own books. By that same token though, you don't get to act surprised when the authorities come a knocking with a warrant to crack open your books when they find out you made a poor decision of people to work/transact with.
Surely you accept that illegal trade happens through cash and even through banks, so you will agree that there is some level at which you cannot ban an entire system.