> why normally anti-establishment and "leave me alone" Americans so sheepishly agree to be involved

Because it's a private system, and it's at least theoretically voluntary. Nobody forces you to get credit cards or borrow money.

Credit cards are immensely convenient. I hardly ever carry cash anymore. I buy everything from coffee to lunch to groceries to gasoline using credit cards, and pay the balance every month. If I had to make arrangements to always carry cash to cover those sorts of expenses, it would be frustrating.