Capitalism is only possible where knowledge is shared unequally. For example, if many people knew how to obtain the proper license or whatever and where to go to buy wholesale, then they would bypass retailers entirely. Similarly, if many people had knowledge about how to start a business and knew several friendly venture capitalists or bank officers, many of them would start their own businesses and there would be few people to do the actual work.
Having said that, I think its important to emphasize some of the things that capitalism gets right: it is still a relatively open and distributed system that is able to evolve more freely than systems that are less so. Open in that many people can actually apply for loans etc. and start their own businesses. Distributed in that there are numerous options and usually no single point of failure.
I don't think that greed is necessarily fundamental to human nature. That's an oversimplification. Humans do need to compete sexually, but I don't think that extreme hierarchies are necessarily a requirement for that. Much of what is considered human nature is just the current state of our culture.
I think its hard to create a system that operates consistently and soundly as a whole but at the same time is robust, distributed and free to develop in different directions.
However, I believe sure that we can improve our current situation by injecting a more egalitarian belief system as well as more science and technology into the power structure and its operating principles, which means the financial system. For example, "economics" is now mainly gaming strategies for maintaining point (monetary) counts and the power that goes with them. But because economics is so critical to human decision making, it must at some point incorporate human needs, social science, and physical science such as ecology. There is a false belief that somehow these monetary gaming strategies and point/goods exchange systems (the economy) incorporate scientific knowledge, measurement, and technological knowledge automatically. That is not the case currently.
One of the problems with all of the systems, capitalistic or anti-capitalistic, is the tendency to move, either quickly or more slowly, towards centralization. When wealth/power as well as goods and services production concentrates it leads to vast inequality, poor distribution, stagnation, inability to cope with local conditions, etc.
I think we need to do a better job of centralizing information schemas and holistic knowledge but do that in a way that does not compromise the ability to evolve those knowledgebases and distribute production or lead towards centralization of power, etc. Its not easy, but I think its a technological problem we can solve.