Back when credit cards had to take paper carbon copies from a subset of retailers that had been certified to take credit, try their damnedest to decipher the faint blue numbers and names, verify the account information by hand, take on significant risk for higher purchase prices due to lower computer capabilities, then process the billing... Yeah, I can see why they charged 3% to every transaction.

Nowadays, all of that is automated and digital and proliferated. There is no reason why AMEX should get $0.50 from every purchase of a Happy Meal. There is also no reason why Visa should get more money from a $20 purchase than it gets from a $100 purchase. It's the same amount of work! Same argument about TicketMaster charging a $200 convenience fee on a $500 ticket but only $100 on a $250 ticket.