At what point does over-use of a term as an insult render it meaningless? Richard Murphy tested the boundary yesterday when he accused John McDonnell’s economic advisor James Meadway of delivering “deeply neoliberal, and profoundly conventional thinking”. This was prompted by a negative comment James made about Modern Monetary Theory (MMT).

In response, Richard posted a list of MMT-inspired leading questions which, wisely in my opinion, James declined to answer. Richard then accused James – and by implication Labour – of not standing up to “the bankers” (including Mark Carney) and remaining wedded to conventional/mainstream/neoclassical/neoliberal thinking (Richard seems to regard these as equivalent terms). Labour is therefore signed up, in Richard’s view, to deliver “more Tory economic policy” and “more austerity”.

This is, to put it politely, nonsense.

At the heart of the debate is the decision taken by Labour, early in Corbyn’s leadership, to adopt a fiscal rule. This commits a Labour government to balancing the books on current spending with a rolling five year target, subject to a “knockout” when interest rates are close to zero. The rule has been a source of contention since it was announced. (I expressed misgivings about its announcement.)

My preference would be for a bit more wriggle room. The two dangers that must be balanced when setting fiscal policy are insufficient demand and private sector unwillingness to finance public deficits. Insufficient demand results in unemployment or underemployment, weak wage and productivity growth, and inadequate social provision. The dangers on the flipside are unsustainable borrowing costs and, particularly if this is countered using the power of the central bank, inflation. The relative weighting given to financial market conditions and inflation in the UK is almost always too high. But this doesn’t mean the correct weight is zero, as less-sophisticated advocates of MMT sometimes appear to think.

The first danger arises when the desired saving of the private sector exceeds private sector investment. In such a situation, achievement of “full employment output” requires a government deficit – give or take the current account. Standard macroeconomics largely assumes this problem away by arguing that, outside of the zero lower bound, interest rates can always be set at a level which will induce the optimal level of demand. Consequently, monetary policy is the only tool required. I disagree with this view: I think it’s quite possible for economies to be demand-constrained and thus require fiscal demand management across a range of possible interest rates.

But on balance I think the fiscal rule has enough flexibility to allow a Labour government to maintain sensible levels of aggregate demand. In any recession in the foreseeable medium-term future it is hard to imagine that interest rates will not be cut to near zero. In this case the rule will be suspended and fiscal policy can be used “with all means necessary”. Second, the rule doesn’t preclude significant increases in government investment spending – a central part of the Labour policy programme. Government investment spending is likely to have strong multiplier effects and should help to rebalance demand in the UK’s consumption-driven economy. Finally, the rolling five year window allows for adapting the pace of current spending to negative economic shocks.

I can also see good political reasons for the rule. It provides an immediate rebuttal to those who try to perpetuate the deeply dishonest but highly successful Tory strategy of depicting Labour as the party of fiscal irresponsibility. As I understand it, the rule was formulated by Simon Wren-Lewis and Jonathan Portes, two highly credible progressive economists. Simon has been one of the most consistent and articulate critics of Tory austerity. To accuse them, as Richard is doing, of “delivering neoliberal thinking” is ludicrous.

Aside from the straightforward inaccuracies, there is a deeper problem with Richard’s argument. He equates, as do some MMT advocates, radical or progressive policy with fiscal policy. There is no question that Labour’s economic programme would mark a decisive shift in macro management: it would be the end of austerity. (Austerity was never really about managing demand and debt, in my opinion: it was cover for the ideological aim of shrinking the state.) But the truly radical aims in Labour’s programme – although not yet fully fleshed out – are on the supply side: structural reforms, but not of the sort pushed by the IMF.

There is merit to this approach, in my view. Yes, the UK economy is demand-constrained. Aside from the direct human costs, austerity has almost certainly done long-run damage to the supply-side. It must end. But over the longer run the UK faces profound challenges from an ageing population, wide geographical disparities, and the potential risks and benefits of automation. It makes sense to focus on the supply side: to have an industrial strategy. A progressive supply-side policy is not an oxymoron. (I remain concerned about how such a programme can be reconciled with a hard Brexit, as some on the Left advocate.)

I have more sympathy with MMT than James. I see it essentially as a US-focused political campaign based around a single policy: the job guarantee. I am not convinced by the policy, but it is the focus of progressive economic and political action in the US. Stephanie Kelton has done an excellent job of debunking simple deficit scaremongering. But to claim, as Richard is doing, that rejecting MMT means accepting wholesale neoliberal orthodoxy is silly – as are several of the views that Richard attributes, without justification, to James.

The left deserves a better standard of economics debate.