What seems at issue -- besides whether an economist's work should be accepted at face value -- is under what conditions a country should borrow or impose austerity.

Here's an analogy --

When times are good, governments frequently raise taxes, because hey, we can afford it.

When times turn bad, governments frequently raise taxes, because hey, our tax base has eroded and we need it.

It's a "heads I win, tails you lose" game.