Cash can be and is tracked. This takes it a step further. I won't be surprised if governments outlaw the use of tumblers or go after everyone with tainted bitcoin (which given a possible high percentage of dirty bitcoin would make them unfeasible). Otherwise, you've given for-profit cybercriminals the last piece to routinely execute perfect crimes.

The usage of tumblers is "money laundering" in mostly every country.

> go after everyone with tainted bitcoin

How? What for? owning tainted bitcoin isn't illegal and given the amount of "tainted" coins it's probably not even enough for probable cause.

Well, effectively outlawing tumblers involves investigating people that pay with tumbler-tainted coins. I mean it more in a Patriot Act type legislation sense rather than probable cause [0]. Obviously, if you've got non-tumbled coins with a direct criminal taint then I'm pretty sure that's probable cause already. Just to be clear - coins are not forever tainted in such context. i.e. someone extorts 1 BTC, the victim reports it - it's now tainted. The criminal pays the 1 BTC for pizza, police arrests him. The coin owned by the pizza place is a clean coin again now.

[0] tho I guess in some cases it could very well fulfill it (>50% probability of a crime having been committed)

To be fair, money laundering is associated with cash in countries where people mostly pay with plastic. Admittedly, the reverse association is fairly weak, as I doubt that bringing up cash will make people think of money laundering all that often.