Greek banks bought about 15B of this Greek debt, which is over half of Greek GDP. This is likely the savings and pensions of a lot of Greek people. There will b

Greek banks bought about 15B of this Greek debt, which is over half of Greek GDP. This is likely the savings and pensions of a lot of Greek people. There will be bank runs (much worse than now). There would be looting, burning, and massive chaos. It would be like destroying 8 trillion in people's savings in the US and just hoping it all works out. It would be a catastrophe. Then, once this destroys the economy, getting any outside investment to help will be impossible, because no one would want to invest or loan to a place that so willingly shrugs off repayment. This is why the situation is such a problem. Just unilaterally ignoring repayment destroys the Greek economy much worse than it is now.