Communism for example wasn't meant to be used as a political structure but an economic structure, you can have pure communism ECONOMICALLY in a democratic environment. More importantly you have to be careful on how you dictate what's "capitalist" America is a capitalist country but we're a FREE MARKET capitalist country, not all capitalism is the same there are sub-divisions to capitalism just like there are subdivisions to company, religious sects, infrastructure, etc. Free market has a Laissez-faire approach where it is made by the consumer and the producer in question, which, in most cases is how America operates. Conservatives believe in free market, however, they believe the money should be reallocated to the businesses so that way when businesses make money they can trickle down the remainder to the people, while this would work with honest businesses it doesn't work for everyone. No form of government is perfect, it depends solely on the people or the person running, there are UPS and downs to basically everything. If there was no greed in capitalism, a country would go very broke, very fast. Due to some monetary means not being met, a form of greed is adopted just to maintain the status quo, it isn't greed of the righteous for sure, but it isn't greed of the unnecessary either. It is a misconception however to generalize that the rich and wealthy oppress the poor, the poor oppress the poor just as evenly, governments rely on the people's ignorance in order to achieve a certain reaction or to further it's goals under normal circumstances. People continuously forget that the power of government rests in their hands and yet many refuse to take action, leading to an array of corruption, to continuously blame someone else instead of yourself has been a game of "hide-and-seek" with humanity and it only shows a lack of integrity, as president Kennedy once said "Ask not what your country can do for you, but rather what you can do for your country".
