Eventually, they might decide to capitate the barber, paying him ten dollars per member per month. Suddenly, the dynamics have changed. The barber gets his ten bucks whether he cuts your hair or not. His incentive is to avoid cutting your hair or, if you insist, on not providing you with any extras. And, of course, all barbers get paid the same whether they are Hollywood stylists or recent graduates of a Marine Corps chop shop.
Health care is more serious than haircuts, but the underlying economics are the same.
If the consumer pays directly, there is a reluctance to part with money and that reluctance controls the cost. This is true regardless of the kind of third-party payer involved employer, insurer, or government. No third-party payer is willing to write a blank check. They will all find a way to limit their costs by restricting the supply of services available to the consumer. They might limit the number of licensed providers, use waiting lists, ration the kinds of services available, deny service based on medical necessity, or prevent certain groups such as the elderly from receiving certain services such as transplants.