If you are familiar with this blog, you will know that I regard 2010 as a fateful year for the advanced economies in their recovery from recession. That was the year that the US, UK and Eurozone switched from fiscal stimulus to fiscal contraction. Because we were at the Zero Lower Bound (ZLB), this policy switch is directly responsible for the weak recovery in all three countries/zones. A huge amount of resources have been needlessly wasted as a result, and much misery prolonged.
This post is not about justifying that statement, but taking at as given and asking what should we conclude as a result.  To answer that question, what happened in Greece (in 2010, not two days ago) may be critical. To see why, let me paint a relatively optimistic picture of the recent past.
Greece had to default because previous governments had been profligate and had hidden that fact from everyone, including the Greek people. Recessions rather than booms tend to be when things like that get exposed. If Greece had been a country with its own exchange rate, then it would have been a footnote in global macroeconomic history: fiscal stimulus that had begun in all three countries/zones in 2009 would have continued (or at least not been reversed), and the recovery would have been robust.
Instead Greece was part of the Eurozone, a monetary union that had been implemented in such a way that it was particularly vulnerable to the threat of default by one of its members. Policy makers in other union countries prevaricated, partly to protect their own banks, partly because they worried about contagion. The ECB refused to act as a lender of last resort - we only got OMT in 2012. So the Greek crisis became a Eurozone periphery crisis. (For more detail, based on an IMF evaluation of their role in this affair, see this post.) This led to panic not just in the Eurozone but in all the advanced economies. Stimulus turned to austerity. By the time some in organisations like the IMF began to realise that this shift to austerity had been a mistake, it was too late. The recovery had been anemic.
Why is that an optimistic account? Because it is basically a story of bad luck, which we have no reason to believe will be repeated again. When the next crisis comes along, the Eurozone will have OMT in place, and hopefully there will be some rational system for deciding when a Eurozone country that gets into difficulties should get ECB help or should be allowed to default. If this was just bad luck, we do not need to rethink how macro policy is made.
Now for the pessimistic version. The political right in all three countries/zones was always set against fiscal stimulus. It is true that during 2009, when no one was sure how bad things might get, Germany enacted a modest (if fairly ineffective ) stimulus, but in the US and UK the political right opposed it. Without Greece, we still would have had a Conservative led government taking power in the UK in 2010, and we still would have had Republicans blocking stimulus moves and then forcing fiscal austerity. The right’s strength in the media, together with the ‘commonsense’ idea that governments like individuals need to tighten their belts in bad times, would mean that opposition to austerity within the political elite would be lukewarm, and so austerity was bound to prevail. While we might hope that this right wing opportunism does not happen again during a future crisis, there is no clear reason to believe it will not. Greece may have just voted against austerity, but there is every chance that in the UK the Conservatives will retain power this year on an austerity platform and the Republicans are just the presidency away from complete control in the US.
If the pessimistic account is right, then it has important implications for macroeconomics. Although it may be true that fiscal stimulus is capable of assisting monetary policy when interest rates are at the ZLB, the political economy of the situation will mean it may well not happen, and that instead we get the fiscal instrument moving in the wrong direction. That means that macroeconomists have to start thinking about how to fundamentally change the way policy is done at the ZLB.
When some economists over the last few years began to push the idea of helicopter money, I was initially rather sceptical. The scepticism could be summed up by saying that helicopter money when you have inflation targets is identical to tax cuts plus Quantitative Easing (QE), so why not just argue for an expansionary fiscal policy? (There was also the point that tax cuts might be a rather poor form of stimulus compared to, for example, bringing forward public investment.)
However, if the pessimistic account is correct, then arguing with politicians for better fiscal policy is quite likely to be a waste of time, a lost cause. A more robust response is to argue for institutional changes so that politicians find it much more difficult to embark on austerity at the ZLB, or to allow others to effectively offset this austerity if it happens. Central banks have QE, but helicopter money would be a much more effective instrument. To put it another way, central bank independence was all about taking macroeconomic stabilisation away from politicians, because politicians were not very good at it. The last five years have demonstrated how bad at it they can be. However that move to independence was always incomplete because of the ZLB problem. We now need to make it complete.
This of course raises all kinds of questions. Do we want to give additional powers to the central bank, or should another independent institution be involved? If we do give central banks more power, could this be limited to enforcing a dialogue between central banks and government (along the lines suggested here), or should we go for something like helicopter money? If the latter, what are the knock on consequences to ensure the central bank can always tighten policy as necessary? Going down that road must in my view include thinking about how to make central banks a lot more accountable, so that they do not behave like the ECB. Arguably macroeconomics has been naive in suggesting that the more independent a central bank is the better.
However, we only need to go there if the pessimistic interpretation of the last five years is correct. Should we put the last five years down to bad luck, or to political economy forces that will not go away. I currently think the pessimistic interpretation is more persuasive, but I will be very happy to change my mind.
 Many argue that the recovery was weak because the recession was caused by a financial crisis, and it was always going to take a long time before banks would start to want to lend again. Even if you put a lot of weight on this argument, it implies a multiplier of one, not zero. It does not justify reducing public spending and employment i.e. making people unemployed when there was little chance they would find work in the private sector.
 The stimulus focused on tax cuts, which are less effective than increased government spending because some of the tax cuts will be saved. See Carare, A, Mody, A and F Ohnsorge (2009) “The German fiscal stimulus package in perspective” VoxEU 23/01/09.