From a more practical perspective, concentrating wealth in the hands of a few people will cause inefficiencies. Rarely does a single person (or a small group of persons) have the best ideas on how to allocate resources. An important tenet of Capitalism is that fair competition breeds multiple solutions to the same problem. While it's inefficient because some aspects are duplicated or tangential (accounting/marketing), it is an excellent system for insuring the best players are providing products and services.