Capitalists perform a very valuable function in society, and one that lacks in any kind of socialist society and which ultimately always leads to its demise. This has been described in many works, but foremost in Ludwig von Mises' works.

In capitalist society there is no director directing capital from above. Instead the free market functions as a mechanism that naturally brings resources there where they are most useful. For example, suppose we have a large country, and harvest in the east fails and there is a scarcity of food. People in a capitalist society will want to pay much to stay alive, and producers of food will want to get food there as quickly as possible in order to capitalize on this increased market price. A potato may be 10 cents in the west, but 50 cents in the east.

In contrast, if there is scarcity in an organized society it is up to the organizer to detect this. This usually works fine. It is not very hard to detect where there should be more food and where there should be less. It is in the subtleties where this goes wrong. Definitely you can ask people how much food they need and calculate when to get it there. The problem occurs in many layered industries. How is a director supposed to decide how much steel to allocate to the tractor factory, to the constructors, to the railway builders, to the automotive industry, to the small tools manufacturers, to the nail and screw factories, etc etc. In the free market society there is no need to think about these problems, they fix themselves. Market prices are determined for steel and producers outbid eachother to get the resources they need. There is no way to do market calculations in the socialist society, as has been proven many times, and therefore such market mechanisms are not possible, neither in theory nor in practice.

This is also why socialist societies are breeding grounds for black-markets (free markets). Volumes have been written about the underground economy in the soviet union. In the DPRK there is a thriving black market for sweets, which are underproduced and in great demand.

It is also worth noting that monopolies occur because of, not despite, regulation. Regulation allows big money corporations to put their fingers where they don't belong: politics. Name me a monopoly or market failure and I'll name you a case of state intervention.