Work is forced under capitalism. See, there are these things like "food" and "shelter" that cost money. You sorta need those to live. So, you either work, or you die.

How do these things change under socialism? Capitalism allows one to work hard, and then reap the benefits of their labor. Capitalism allows people to gain from their work, and therefore increase their well being and happiness.

Socialism allows one to work hard, and then have everything in excess of what they need be taken away from them. Socialism does not allow anyone to gain from their work, and instead puts them in a situation where they have to work. They are less happy, their well being deteriorates.

To say that either of these systems allow anyone to slack off and continue to have a happy and fulfilled life, is blatantly incorrect, not to mention utopian.

... there is a natural economic system. It's called the barter system, and there's some damn good reasons why we don't use it anymore.

We have certainly moved on to better things, but the concept remains the same. Currency has simply become the medium between trade.

The free market was coined by a dude named Adam Smith as a critique of mercantilism, the then-dominant school of economic thought. What he meant by it was essentially free trade between nations and their colonies. Back then, it was standard practice to ban your colonies from trading with people other than you, you see.

Your right! Adam Smith simply defined capitalism. He gave it a name. But you have to go further back in time. Before the world was ruled and regulated by Monarchs and Government. The simple idea of capitalism is, as you mention, free trade. Free trade has been going on since the human tribes began to swap items with each other in Africa, and most likely before that as well. Free trade is the reason for the massive progression away from tribalism and commune-like living.