If you had that kind of situation with Bitcoin, it would be a problem. You might receive Bitcoin from someone who received it from another person, and that person received it from someone, who stole it from Mt. Gox. Then some exchanges can say, that they don’t want this Bitcoin and they may even shut down your account. That might be a big problem.
I believe this to be mere speculation. In the case of fiat, the authorities trace back the stolen cash by repossessing the left over cash and the assets that have been bought by the offender using the stolen cash.
If the cash has been used to buy property the authorities go after the property and do not trace the cash so as to reposses the cash from an innocent seller of property to the offender. The law I am sure will apply the same principles when it comes to cryptocurrencies.
Yes, but with UTXO its "easier" to trace that money (BTC) than paper notes. But let´s see the future.
The issue I am referring to is not about the difficulties of tracing; I am saying that generally the law doesn't allow recovery of money from innocent purchasers unless the purchasers were complicit in the illegal transaction.