[cwkoss]

Tumbling is plagued by a horrible tragedy of the commons problem: the more tainted your coins are, the more you want to tumble them. People who legitimately acquired their bitcoins don't need to tumble them, so chances are you are just getting other tainted coins in return.

People seem to think that coins are 'clean' after tumbling, but I think its much more likely that you'll get back more suspicious coins: superlatively, "Here's my personal-use drug bitcoin, give me coins that were earned by assassinating someone"

[manfredo]

Isn't the whole goal of tumbling to provide plausible deniability? The goal is to avoid tying the coins earned or used in an illicit activity with the the people involved in those activities. If a drug dealer gets an assassin's coins and vice versa then the goal is still accomplished even though all the coins involved are tainted. The drug dealer's possession of the assassin's coins don't help in building a case against his or her drug dealing operation.

[cwkoss]

True, but being in possession of coins tied to an assassination probably puts you at greater risk of being the subject of a federal investigation than being in possession of drug-related coins.