In an article titled 'Get merchants to lust after credit and debit card acceptance!", Aneace Haddad writes on his blog about how merchants feel about credit and debit card acceptance - and "why merchants and regulators are fighting interchange fees so fiercely." His "worst case scenario" is pretty dark for the card industry: "merchants win their antitrust lawsuit, banks lose $100 billion, interchange revenue is eliminated and banks have to pay merchants to accept cards."
Another point of view might be that all of those credit losses that card issuers suffer consist of sales actually made by merchants. One can argue that US card accepting merchants' top line sales revenues are about five percent higher than they otherwise might be - after all, that's roughly the level of credit losses currently being absorbed by credit card issuers.