Theoretically, assuming that the mixer is perfectly implemented and law enforcement never uses their legal authority to compromise it, and that your records are never acquired by law enforcement.
There's no reason to believe any of those assumptions are true – and once any of them fail, you've helpfully given the prosecutor a detailed, hard-to-deny log of your every transaction.
It'd take effort for a mixer to log things - it's not something that happens by itself. There's no reason to think the implementor would do that, unless the mixer is already compromised.
Other than that, there's really not that much to implement in the mixer.
Additionally, the break in security is disjunctive. It's not just the mixer that has to be compromised, its the entire chain - exchange, wallet, mixer; if any of them do not cooperate, your trail ends.
> It'd take effort for a mixer to log things - it's not something that happens by itself. There's no reason to think the implementor would do that, unless the mixer is already compromised.
This is true in theory but the history of software is littered with obvious counterexamples where theoretically secure software was compromised by admins forgetting to disable debugging / logging, insecure temporary or backup files, etc. When you use a mixer you're trusting the admins to get all of that right even before you talk about malice.
I'm not saying it's trivial, merely that the bitcoin infrastructure was obviously not designed to counter state-level threats. The perfect identification of all past transactions is just too easy to get wrong and and a prosecutor only needs to show a convincing case, not absolute mathematical proof – I wouldn't bet against the simple timing of transactions being enough in many cases
True, but will someone really spend hours following your bitcoin trail across the internet getting subpoena's for your information at numerous exchanges and mixing services you put your coins through. When there are literally millions of people downloading illegal content in the clear?
