Oh, at first sight I was tempted to take this approach for a cure of my worries about bitcoin's anonymity.

Imagine exchanges would not refuse tainted coins right out but "untaint" them by sending the tainted fraction to a well known unspendable address (aka destroy the stolen coins). A future recipient would well notice the tainted coins but also the untainting and accept the input for full bitcoins again.

Imagine gox doing this. Who would want tainted coins? All others would follow and refuse to take tainted coins aka untaint them and demand compensation for the tainted fraction of the payment.

I could imagine such a system for the good of bitcoin as the scheme "move your coins -> claim to got hacked -> profit" would get eliminated and bitcoin would be ultimately more secure but I have a problem to decide who should judge which coins are tainted and which not.

Imagine somebody selling bitcoin and only getting 70% of the promised [dirty something]. He could claim he got hacked to piss off his business partner who would not go to a court for [dirty something].

In a case as yesterday, I see no problem to count bitcoins as stolen and therefore nonexistent/invalid. But what if the raid is discovered only 3 months later and many people already accepted them? What if gox is forced into blacklisting coins from Iran? Etc ...

I love these thought experiments but I would prefer it were easier to say once and for all coins will never be tainted. Else mining would be the only way to get clean coins for sure. Mining where I get the created coins ... from blocks without fees