err mastercard/visa not hard to deploy infrastructure????
What planet are you living on?
here's a thought experiment for you:
Go to South Africa. Use your non-mastercard non-visacard payment method to buy a loaf of bread.
Then go to Australia, use your non-mastercard non-visacard payment method to pay for a taxi ride.
Then go to america, use your non-mastercard non-visacard payment method to buy a plane ticket.
Then, after they all deny your payments because they don't support google checkout, because they haven't received the Credit-Card processing machine that supports "Western Union" tell me there is no already deployed infrastructure that is required to process your payment.
Fact is, they deploy hardware. Those little mag-stripe readers are designed to work with them. If you killed mastercard, and visa, all those banks that process those cards would stop being interoperable. You could still use BankX card at BankX machines, but unless BankX talked directly to BankY, you now can't use your card there. You'd need 2 cards.
You see, what mastercard and visa do, is they have deployed a world-wide system, that gets banks to sign up to, to then allow credit cards issued by BankX to work at BankY machines, and vice versa. While it may not be all "Hardware" infrastructure, it is "Software" infrastructure. Legal infrastructure even if you will. BankX agrees that when MasterCard says "Charge it" BankX pays the merchant the money. even if it is a BankY card!!.
Your example of Mastercard or visa denying a card to someone? Actually a false example.
BankX is well within their rights to deny you a card.
BankY is well within their rights to deny you a card.
Neither of them can deny you a card: "For being smelly". Often you'll find they need to provide an actual reason for denying you the card. And if they do, you take them to court and a judge will agree. Double the payout when it turns out both BankX and BankY spoke to each other and said: "I'll block him if you block him" and it turned out the whole reason they decided to deny service was "because we don't like his beliefs about how the world should work".
(as opposed to: "we thought he would be a bad debtor". You can deny bad debtors loans, thats a stupid counter-example).