[panarky]

> when the debt level becomes unsustainable

I'm arguing that you can't determine what the unsustainable level of debt is for the world in total.

Yes, debt can be unsustainable for a family, or a company, or a nation.

But if I, as a creditor, decide to risk my capital by lending to my neighbor, or to the United States, that increases total world debt, but it's not necessarily bad or dangerous.

In the case of Greece's debt crisis, the important question is why creditors lent too much to a nation that couldn't pay it back.

There are many answers from ignorance to failed governance to corruption, but none of the answers have anything to do with the general level of debt in the world as a whole.