Earlier quoted context omitted.
Bitcoin addresses for darknet marketplaces are easily available - e.g. https://www.walletexplorer.com/ Perhaps Coinbase will turn you away if they see you depositing money on a drugs market?
It is ironic that Bitcoin is thought of as the criminals currency when it's one of the most trackable in the world.
With untrackable currency (USD, et al.), you get HSBC's and all the others, who may commit crimes in secret and destroy the evidence.