Capitalism is superior to socialism because it creates an economic rather than a military arena for competition. Socialism destroys wealth by not fostering economic improvement. A socialist's only recourse is to improve by imperialist expansion, or warfare. Capitalism, meanwhile encourages all participants to compete to generate more wealth in a peaceful way.
Usually when will talk about capitalism we think about American Industrial and financial might mostly bought about by a thriving Democracy. Milton Friedman is the most influencial man in the 20th century in regards to the U.S. Economy. Friedman promotes economic freedom as both a necessary freedom as well as a political on. Without political freedom and a gov't to wield proper oversight over our economy and finances thing will get drastically bleak much like how it is in N. Korea.
Although capitalism represents the free side of society, socialism effectively reduces the chances that conflicts will happen within the country. Looking at the US, the king of capitalism, we are a very volatile society with many fearmongers and a giant army. With a socialist society in place, it would force each citizen to conform to government regulations, and although it would still be volatile, those feelings would be contained by the government.