[rspeer]

Let me give you some more parsimonious paranoia: the tumbler operator is likely already working for the government, or accepting money from governments to forward them DumbSeller's transaction history. Why would they not?

Running a tumbler seems like a great racket if you can cope with the amorality (and particularly if you can rationalize the fact that you're sending money to ISIS with probability approaching 1). People pay you fees in exchange for "privacy", and have no way to tell if they got it.

If there exist tumblers that don't sell their customers' transaction history, in the ruthless capitalist world of Bitcoin, they are easily outcompeted by the ones that do. And a tumbler "customer" has no way to shop around for privacy.