Earlier quoted context omitted.
It only takes a few countries imprisoning people who trade in tainted coins/tokens before they become untouchable. Public ledgers are public. If the US IRS, perhaps coordinated with Interpol, publishes a blacklist of coins, those coins are toast.
Uh, so wait. If the IRS/Interpol becomes an effective source of truth on which coins may be legally transferred and who rightfully owns them, what was the point of the blockchain?
At the very least, the blockchain provides a degree of global immutability that was previously impossible.