The reason is because out of the three parties to the transaction, only one of them is fraudulent. That is the so-called lender. You, the customer, are producing value with the hard earned money you are paying; and we, the merchant, are providing value with our hard earned product. It is ethical and sound thus far. We should be paid and you should receive good value, rightfully so. It is when the international crime syndicate called the money lenders insert themselves into the middle of the transaction and attempt to extort their cut, that we draw the line. No money came out of their accounts to issue the loan -- it was created out of thin air using the Mandrake Mechanism -- and no value came out of them either, in the way of goods or services.
One could argue, well, they provide the medium of exchange -- i.e. the money, and administer that system. If so, then the honest way to do it would be for them to charge a small nominal fee, such as 0.01% of every transaction worldwide, for maintaining the money system. That might be fair. It would be open, honest, transparently visible, and mutually agreed upon by everyone. But paying "back" 100% of the value of the transaction PLUS usurious interest, is nothing less than outright theft and extortion. It is a parasitic influence on the global economy and has destroyed countless lives. That is wrong and must be stopped.
We are not harming anyone or taking anything that isn't offered, by accepting credit cards to pay for our products. On the contrary, as sovereigns, we are exercising our God-given right to transact in commerce and provide our goods and services using whatever medium of exchange society has most agreed upon. The fact that a corrupt cabal has tried to insert itself as a fraudulent party to the transaction is the reason for our withdrawing our support from that behavior.
Further, for every debt cancellation system we sell, and for every debt cancellation system a new customer implements, the economy is improved by that much. The economy is improved because money that was otherwise going to the international crime syndicate -- which they then use to hire armies of mercenaries to organize the banking and court systems against us -- is money that is now going instead to one's own (presumably) harmless and life-supporting home living and household expenses and perhaps education or creative and constructive projects. It is withdrawing money from what is harmful in the world and redirecting it to what is helpful. That is a most beautiful fulfillment of the purpose of ethics.