They are providing the service of making your money available for payment without you having to think about the logistics of moving the money (plus credit facilities, chargebacks, fraud protection (If I have a wallet full of money and someone spends it I'm down that cash. If I have a wallet full of cards and someone spends with them, I'm covered.)). It only seems fair that they get paid for their work.
Whether the amount they charge is worth the services they provide is another question entirely.
You are completely missing the point.... I at no point suggested that they shouldn't charge.
That it is a percentage of the transaction amount is what I have a problem with. If their business was truly about "credit" they shouldn't need extra charges as they claim back more value from bigger loans/transactions.
Debit cards provide the same service without a percentage charge but without the payment protection. Its a rigged game.
