The reason why credit costs more for merchants is because the interbanks get paid most of the interchange fees (interest and transaction fees) and the credit procesors Visa, amex, mc get paid the association fees. But the banks cover most of the costs in case of fraud and stolen cards and accounts and most customers are not liable if the transactions are abided by the rules of the credit card companies. They know this happens alot and to keep commerce moving with more sales this is a built in "expense".
I think you misunderstand the status quo
Fraudulent Transactions
The most common cause for chargeback is fraudulent transactions. This happens when the credit card is used without the authorization and consent of the cardholder. In cases like these, the merchant is held solely responsible.
https://www.dalpay.com/en/support/chargebacks.htmlBitcoin provides a great advantage to the merchant in knowing that when they are paid, they are paid and when they ship their $1200 item out the door, they won't end up doing so for free.
Of course, this potentially puts the purchaser at a degree of risk. Expect to see commercial escrow services or merchant guarantors arise to take care of this.