Money needs to be fungible to be widely accepted ... if some BTC is deemed to be "cleaner" than others then it is no longer fungible.
Of course, people shouldn't scam or steal or money-launder or sell slaves or whatever ... but it is not the job of the money to decide who is right and wrong, it is just an accounting token for facilitating trade and commerce, it is not legislature, police, judge and jury.
We need a blind signature layer so that BTC can be fungible and do a better job of being money. (Some digital sheriffs or bodyguards wouldn't go astray in this wild west either it seems ... or even a posse or two.)
Bitcoin is acting as money, it is simply that one property of bitcoin is that all transactions are public, there is a record. This is what makes it so difficult to double spend (and other bad things)with bitcoins, it is what makes it a p2p currency.
Bitcoin is so new there is nothing like it, it has some of the same properties of fiat money(cash), gold, and digital money(in real bank accounts) all at the same time. This means that bitcoins can be traced if they are not laundered.
Think of it in terms of bank accounts. Money was transfered from a number of bank accounts to one in a scam. The bank has those records(in our case the block is the bank, and the record of the transaction is in it). The person with those funds has now transfered them to an account owned by MTGOX, who is a banker. He can see these records, and decides to freeze all the related funds to investigate.
We don't have the final conclusion,decision,result. MTGOX is still investigating, and when he is done I am sure he will make a statement with plenty of details.
Because the exchanges are really the only real exit from bitcoins (and lets be honest here, scammers are after cash not bitcoins) unless you consider OTC, but I don't think anyone in #bitcoin-otc would touch dirty bitcoins, especially with someone who has no or little reputation, which a scammer would.
This puts the exchange operators in a powerful possition, they become the ones who CAN do something about stopping scammers, while most of us can do nothing. They are not obliged to act, but we can see here that MTGOX thinks this is worthwhile. If he thinks it worthwhile I would think it must be. He has my trust, and the trust of many here.
This is how we, as a community, as an economy can protect ourselves from scammers and cheaters. It is non-violent, such as boycotting, confiscation of assets that have been entrusted to society members(remember if you give someone possesion of something, you give them power over it). It is also efficient. Much more so than a court.
You coud set up an exchange, and guarantee that no such thing would ever happen on that exchange, that you don't care about the history of any bitcoins and would not stop anyone trading. But then all the scammers would flock to this exchange. And all the good users would know this, and not use it. So it would become an exchange for scammers and no one else. And they would be kept away from the rest of the bitcoin economy.
I think this is good news for bitcoin, it is showing that scammers (twice now) won't be able to get away with their crimes. That the chance of them succeeding is getting lower all the time, and the work they must do to scam is getting harder all the time. This will only make the bitcoin economy stronger and more trustworthy.
I'm looking forward to MTGOX's story.