The macroeconomic case for not cutting the deficit straight after a major recession is as watertight as these things get, at least outside of the Eurozone. (It is also true for the Eurozone, but just a bit more complicated, so its easier to just focus on the US and UK in this post.) If you want to bring the government deficit and debt down, you do so when interest rates are free to counter the impact on aggregate demand. As the problems of high government debt are long term there is no urgency for debt reduction, so the problem can wait. The costs of fiscal consolidation in a liquidity trap are large and immediate, as we have experienced to our cost.
Sometimes austerity proponents will admit this basic macroeconomic truth, but say that it ignores the politics. Politics means that it is very difficult for governments to reduce debt during booms, they say. Although it would be nice to wait for interest rates to rise before cutting the deficit, it will not happen if we do, so we have to cut now. Like all good myths, this is based on a half truth: in the 30 years before the recession, debt tended to rise as a share of GDP in most OECD countries. And it always sounds wise to say you cannot trust politicians.
However both the UK and US show that this is not some kind of iron law of politics. In the UK debt came down from over 100% of GDP between the wars to less than 50% of GDP by the mid-1970s, and was lower still before the recession. (Debt was lower before the recession than when Labour came to power in 1997.) US debt also fell sharply after WWII, but rose again under Reagan and Bush, fell under Clinton and then rose again under the other Bush. So the empirical evidence on US and UK debt is not that it is inherently difficult to reduce in booms; it is do not elect Republican presidents.
My reason for returning to this issue was thinking about the post 2015 UK election plans of all three main political parties. As I have outlined before, all involve tight fiscal control - in my opinion tighter than would be prudent from a macroeconomic point of view. This is fully six years after the recession. So it looks like politics is capable of promising fiscal consolidation well after a crisis. Are we meant to believe that if instead of austerity we had had additional fiscal stimulus after the recession, within the framework that Jonathan Portes and I suggest, things would have been quite different by 2015?
 It is true that no party is - as yet - telling us exactly how these numbers would be achieved, but this does not mean it will not happen: the Conservatives delivered in 2010, and Labour broadly stuck to its fiscal rules until the recession. The only party to go back on their election promises were the LibDems, who campaigned for less austerity than they ended up delivering.