I'll refer the religious capitalist wonks to my earlier post on the nature of Bitcoin:
Suffice it to say that such large, amazingly outperforming oligolies are extremely difficult to form on completely unregulated markets.
Bitcoin itself is an oligopoly. What are Bitcoins made of anyway? They're just bits, information, and by themselves information is incredibly, ridiculously cheap. Of course the incredibly low price of information is made possible by the free market itself, specifically the amazingly successful computer industry.
Bitcoin is a system by which every participant creates a shared oligopoly on a particular set of information, the blockchain. From day #1 Bitcoin was about taking information that, if subject to free market forces, would be so incredibly cheap that it'd be basically free and artificially making it expensive. This shared oligopoly, achieved through the rules set out by Satoshi, makes this information incredibly expensive, so much so that 32 bytes of information, a private key, can now be worth millions of dollars.
Basically the decision about how big our shared oligopoly should allow blocks to be is just a decision about what rules we'll follow to make our little bits of otherwise worthless information as valuable as possible. Myself, gmaxwell, and many others happen to think that if we limits blocks to 1MiB each, keeping the regulations as they are, our little oligopoly will maximize the value of that information. Gavin, Mike Hearn, and many others happens to think that if blocks are allowed to be bigger than 1MiB, thus changing the regulations, our little oligopoly will maximize the value of that information.
Don't for a second think any of this discussion is about free market forces. Bitcoin is about artificially subverting free market forces through regulation, for the benefit of everyone participating in the oligopoly that is Bitcoin. It just happens to be that the way to become part of this oligopoly isn't by, say, living in a certain part of the world that's mostly desert, it's by either buying entrance (buying some Bitcoins) or by doing a completely made up activity that has no purpose outside the oligopoly. (mining)