The problem with economic systems is that they exclude the "People are selfish fucking bastards" factor.
On paper, they look great. All the factors contributing to the greater whole, and working wonderfully.
However, people are selfish fucking bastards, and if they can, they will work any and all systems to give them the economic advantage. Hence the need for regulations.
Take, for example, the much-vaunted Free Market System.
Ideally, the free market system is supposed to be ruled by supply and demand. When there is a higher supply, there is a lower demand, and therefore lower prices. The reverse is true, when there is low supply, and high demand.
However... Say it with me now: People are fucking bastards. People can either hoard their supply, or order their factories (even though they have the capacity) to only make a very limited stock, increasing demand, prices, and profits.