Re: Socialism & Communism
Apologies ahead of time for drifting off topic on this one.
First off, what you need to understand is that Socialism and Communism are not political systems per se, they are economic systems.
Communism
Communism involves the collective ownership of all property. If you need food, or a car, or a broken leg set, you receive them. If someone needs... whatever it is you do, you do it for them. There is no exchange of money because there is no exchange of value. You willingly do what you can for the good of everyone else, and they do the same, and everyone is happy. It's a wonderful system on paper, but Marx kind of forgot to take into account human nature. You honestly could not get this to work with any large group of people without widespread, religious devotion among them to making it work.
Socialism
What most people think of as communism is actually socialism. The Soviet Union, China, North Korea, Cuba, etc. are not communists, they are socialists, and don't believe them if they tell you otherwise. Under socialism, the state owns all property. Thus my house, and my computer, and my Star Trek RPG books have all been granted to me by the government to fulfill my needs, and I work at a government owned and controlled job to provide for the needs of others. Ideally, there would be no money exchanged under this system as well, because the State manages the production and distribution of all resources. Marx envisioned this as a necessary transitional step towards communism, but nobody has managed to get past the point where omnipotent enforcement of the state is required.
Capitalism
This is the one we are most familiar with. Property is owned privately (meaning my house, my computer, and my Star Trek RPG books are mine, damnit, I worked for them, if you want some, go buy your own), and the value of goods and services is determined by competition, supply, and demand.
In practice, no pure form of any of these economic systems exists on the macro scale. A purely socialist system would require such a massive bureaucracy to micromanage everything that it would collapse under its own weight. A purely capitalist system is open to all sorts of abuse and exploitation. A purely communist system is hopelessly utopian. Thus we see that the socialist systems still rely on paying people money as an incentive to get them to produce, while in capitalist systems the government places legislative controls on trade, and siphons out capital for redistribution to those who haven't "earned" it (hey fellow Americans, what do you think Social Security, Medicare, and the other social programs that make up something like 2/3 of the federal budget are? Quit razzing them furriners about being a bunch of socialists, because we do it, too. :D).
Note that none of these systems necessarily precludes one sort of political structure or another. You could have a representative democracy operating a largely socialist system, or an autocratic dictatorship running a completely lassez-faire capitalism. Some systems just lend themsleves to one government type more than another (since socialism requires totalitarian government control of the economy, it tends to attract a totalitarian government: see the aforementioned list of socialist states).
Communism is supposed to operate under a total anarchy, and since we're being totally unrealistic about human behavior economically, why not do the same politically, right? ;)
In order to stay on the Trek topic, I'd hazard that the Federation operates under a blend of communism and capitalism, mostly due to the level of technology. With matter/antimatter power generation and replicator technology, scarcity of and competition for basic resources has been all but eliminated in the core worlds. This has led to an elevation of the basic value of labor, and a decrease of the inherant value of "items". I would speculate that Federation citizens do actually earn "money" in the form of credits, but that the cost of living is rather low so they don't need to earn a lot. Basic needs are taken care of as a mater of course, and your leasure credit goes a long way, since the value of an item lies not in its manufacture (that's the touch of a replicator button away) but in the act of its creation/design. Which explains why things which can't be replicated are very expensive.
-Chris Landmark
(Who now wonders if the Republicans are gonna show up at his door and take away his party membership for talking like this...;))