There is no reason why the payment processor can't implement some security in case of errors. What is more, with credit cards you are handing out your details every time you do a purchase. Have you ever heard of stolen credit card data? When you transfer BTC your don't need to send all your private details that would permit an unwanted second purchase.
>>Fiat -> BTC -> Fiat adds an unnecessary link to the Fiat -> Fiat transfer. How could this possibly be more efficient?
In a BTC economy there is no need to do the conversion.