ACH and CC networks shoulder the burden of maintaining the system, fraud checks, chargebacks, etc. They provide a convenience function that lets me avoid having to carry cash around everyone, and lets the vendor minimize their cash-related costs. It's all worth the 2-5% they charge (and if you're paying more than that you've got bad negotiating skills). Cash isn't cheap--after security-related expenses, it costs just as much if not more than accepting credit cards, but the expenses aren't as easily traced back to individual transactions.
A guy bringing me a plate someone else cooked has not earned 20% of the bill.
A guy bringing me a plate someone else cooked has not earned 20% of the bill.