Greece's debut is less than what Obama spent on the stimulus plan, so it's not going to do much damage on its own. In fact, as fears of such a default loom, investors move money to U.S. treasuries, which is why the 10-year yield is so low. The risk is that the default won't stop at Greece, but the advantage of everyone using play money is that there can be no real shortage of it.
What gold hoarders (not investors) envision is a collapse of the world-wide economic system, but that would result in the starvation of hundreds of millions if not billions of people. Do you really think that many people are going to sacrifice themselves rather than continue to accept play money and go about their comfortable lives?
Modern economies are based as much in the minds of people as they are in reality. That's also true of gold. You can't eat it, burn it to cook your food or keep you warm, and it doesn't make good clothing, tools or machinery. The idea that it has value is just that, an idea. There's no physical reality to "value" nor a scientific means of measuring value. The value of paper money is just as real in modern societies because the idea of it is engrained in our minds from early childhood.
As ants use chemicals to organize individuals into productive endeavors, humans use money to do the same thing in what we call an economy. Money is really just a means of communication, which is why it can be sent electronicly in any amount.
