Obviously you can get dirty money from a mixer, but the relevant part is that you don't get money from the same dirty source more than once maximum twice. I mean, sooner or later all money will be dirty, somewhere in the chain? That doesn't mean you can convict random people that might have owned the money at some point.
In some jurisdictions, you might be forced to explain the origins and destinies of such money, to prove it was not you who made it dirty. And, very likely in these same jurisdiction, using an anonymizer is illegal by itself. That's what I meant.
If you could break the transaction chain cash wouldn't be the only safe way. Cause it doesn't really matter if people/gov can see that you've got BitCoins that you traded for USD as long as they can't trace where the BitCoins come from. I could just say "Donations from my blog" or whatever.
I mentioned cash because I think the weakest link in bitcoin anonymity is when bitcoins are traded against official currencies, using banks. In the banking system, there's no anonymity. They could find you through your bank account. With cash transactions, that's much harder - harder than tracing bitcoins.
Though I think a lot of people want to be anonymous even though they're not doing anything illegal. That's probably the same people that think 5% for mixers is way to expensive.
Agreed.