The way i understand it, Bob wants to send 1 BTC to Alice, and Charlie wants to send 1 BTC to Dave, and everyone wishes to do so anonymously. Through the wonder of mixing Bob's coin actually ends up with Dave. Unfortunately for Dave, Alice was a drug dealer and Dave gets arrested for receiving stolen property or proceeds from crime or some such.
Except in reality the mixing is done with smaller parcels, and a larger number of users. Whether or not the feds want to go after you for receiving 27c worth of drug money is another matter entirely, but i can quickly see there being some negatives to using a mixing service.
It depends how you write the blacklisting/tainting rules, which may depend on money laundering regulations and legal standards of proof. You can say that transaction outputs are all tainted if one input is tainted (an or rule), outputs are tainted only if all inputs are tainted (an and rule), or outputs taint equals the average input taint. Mixing can defeat two out of three of these rules.
The way i understand it, Bob wants to send 1 BTC to Alice, and Charlie wants to send 1 BTC to Dave, and everyone wishes to do so anonymously. Through the wonder of mixing Bob's coin actually ends up with Dave. Unfortunately for Dave, Alice was a drug dealer and Dave gets arrested for receiving stolen property or proceeds from crime or some such.
Except in reality the mixing is done with smaller parcels, and a larger number of users. Whether or not the feds want to go after you for receiving 27c worth of drug money is another matter entirely, but i can quickly see there being some negatives to using a mixing service.