It is also the only truly moral system of exchange. The basis for capitalism is not greed. You don't see misers creating Walmarts and Microsofts. Think about it for a moment. Capitalism is truly miraculous.
Capitalism is a moral system if only because it is based on trust.
When we turn on a light, we assume that there will be electricity. When we drive into a service station, we assume that there will be fuel. The answer sounds simple, but it is often overlooked in places where you would think they would know better. We succeed as capitalists by offering goods and services that others are willing to buy. Many capitalists do not make correct assumptions about what to offer and fail, but that is as it should be.