... by default ?
What's the benefits of participating in mixing someone else coins ?
Say 98% of users do not have anything to hide and would prefer all transactions be traceable for the benefits of discouraging bad behaviors ?
I would much prefer someone who stole BTCs to pay a fee to shameless mixer than to help him unknowingly.
Bad behaviors like what? Donating to WikiLeaks and other politically incorrect causes?
Do we want Bitcoin to be a system that tracks taint of coins, or don't most of us share the consensus that the system as a whole would be better off without the notion of tainted coins, even if that means a few thieves will have an easier time getting away with their crimes? For everything you're asking for, there's MasterCard.
Tracking tainted coins is already very challenging, As a coin mixer would I bother to do research on every case of stolen coins and act as a judge on every cases,,, for say 50000$ worth of BTC ? probably NO. But say there was a major heist of 500k BTC at a major exchange and the savings of tens of thousands of peoples were lost, putting the whole economy at risk. ?
Or say someone kidnapped some very important person and the life of many depends on finding who spent the coins ?
In those later cases I would rather accept the highest fee of whether the client or the affected peoples. People who got stolen 50 000 BTC would pay a hefty bounty for any information leading to the culprit.
Sorry but I always thought of this as a feature of Bitcoin and I will continue to see coin mixing as a non-issue for 99.99% of honest peoples and 99% of dishonest ones.