The professoriat has been a little too cavalier in arguing that debt does not really matter for the world as a whole because we all owe it to ourselves. Debtors are offset by creditors (not always from friendly countries). Common sense suggest that this academic solipsism is preposterous, and so it now proves to be.
“As modern macroeconomics developed over the last half-century, most people either ignored or finessed the issue of debt. Yet, as the mainstream was building and embracing the New Keynesian orthodoxy, there was a nagging concern that something had been missing…..There are intrinsic differences between borrowers and lenders; non-linearities, discontinuities… It is the asymmetry between those who are highly indebted and those who are not that leads to a decline in aggregate demand.”
Creditors do not step up spending to cover the shortfall when debtors are forced to retrench suddenly. So the economy tanks.