CoinJoin is not a crime

Cash is fungible because nobody asks a twenty where it has been. Chain analysis exists to make sure someone always asks.

Fungibility as a design goal

A coin whose history can be scored is a coin that can be refused. Once exchanges refuse coins, holders start pre-screening, and the ledger acquires a caste system that no protocol rule ever specified.

Mixing is the ordinary response to that, and it is treated as suspicious precisely because it works. The legal exposure is real and worth understanding; the moral confusion is not.