With 7% stolen from MtGox and add to that all the other thefts (known and unknown) lets say right now today 10% in circulation are stolen.
At what point do merchants and users stop buying and accepting them because of the 1 in 10 chance they are accepting stolen Bitcoins?
Will next year be a 50% chance your accepting a stolen Bitcoin?
Even at $10 a coin 5000 bitcoin would be a nice payday for a lot of people in the world particularly because bitcoin is prefenced- stolen bitcoin don't sell at a discount. To put it in perspective, Nigerian banker princes will send out a lot of emails in hopes of earning a few hundred dollars.
And if they did, why would I trust them knowing that?
Any business has plausible deniability- they just point to the blockchains and ask "how can I tell this transaction is in dispute? Anyone can claim anything. I don't see a judge's signature establishing ownership."
Credit card companies can do what they do because of contracts that might make the merchant eat the cost of goods on a disputed claim. The merchant in turn can have insurance against certain types of loss, just as the buyer has such insurance against loss as part of their agreement with the credit card issuer. It's not some digital technology that makes it work. Digital technology has cut the costs, but credit cards worked when transactions were hand processed using paper records.
That's not to say that I think that CryptoCurrency is necessarily going to ascend to the main stream. Theft is a problem because the wonders of the blockchains don't prevent theft. All it does is record the transaction, it judges not. and the lack of regulation and volatile exchange values and potentially catastrophic losses make insurance against loss likely to carry prohibitive premiums or margin calls.