Earlier quoted context omitted.
Payment processing costs are a scam. They're 10x as expensive as they need to be to fund rewards programs and fund the financial system. EU max credit card transaction fees are 0.3%, in the US they can be up to 4%. It just doesn't cost 4% of a transaction to handle the exchange of funds. Just wealth transfer to finance people and the upper class who take advantage of credit card perks.
The funny thing about that is that HN used to say if the fee was 4% it's because that's what it costs and if it was any lower the card networks would just abandon the country that forced it to be lower, since they'd lose money.
Do you have a link to the comment you're thinking of?