There are several different strands of mainstream economic thinking and these differences manifest in the way they think about monetary and fiscal policy. The extreme mainstream position is that fiscal policy is ineffective because it 100 per cent crowds out private spending. The only role for aggregate policy then is to allow an independent (politically speaking) central bank to adjust interest rates up and down to regulate inflation (via expectations). There isn’t much for economists to do if that view was accurate. Then there are mainstreamers who think that budget deficits are generally damaging to private spending because they drive up allegedly drive up interest rates and crowd out private spending, the latter which, is considered to be more efficient because it is backed by the so-called wisdom of the “market”. So generally monetary policy should be used to stabilise aggregate demand such that inflation is stable. However, this group of economists find some time for budget deficits when there is a “liquidity trap”. From the perspective of Modern Monetary Theory (MMT) – whether there is a liquidity trap or not is irrelevant.