It is hardly advanced political science to observe that governments are more popular when giving people stuff than when taking it away. Junior doctors, who are getting a pay rise, are probably better disposed towards Keir Starmer and Rachel Reeves right now than farmers, who are losing a tax break.

Not all farmers. The government says its reforms to agricultural property relief (APR) and business property relief (BPR) will mean inheritance tax is levied on about 500 estates that were previously exempt. Agribusiness lobby groups say many more will be affected, potentially 70,000. Farmers have marched on Westminster to vent their fury.

Dispute over the numbers is largely a function of different ways of measuring the “impact” of a tax. One dead farmer could bequeath assets to many people, not just a spouse and children. All might be affected – financially and emotionally – by the prospect of a bill from the exchequer. None of them will be happy to sell land that they had expected to inherit tax-free.

It is also feasible that the Treasury has not fully modelled the way the two reliefs being adjusted – APR and BPR – work in combination with each other. It may have undercounted the number of farms whose value on paper has risen steeply as land prices have soared. But that latter point could be construed as a defence of the new policy. The extra millions of pounds added to the value of an asset by nothing more innovative or enterprising than the passage of time is exactly the sort of unearned windfall that a fair-minded taxman should be raiding.

Even if the true number of farms affected by the proposed changes is higher than official estimates, it will represent a tiny fraction of the total number of estates annually covered by inheritance tax. The rate will still be half of that paid by non-farmers, and there will be more time to find the money.

In the wider context of inheritance tax (which accounts for just 0.7% of all tax revenue), agricultural land will still be privileged, only not quite so much. This is not how the issue has been projected into the public arena.

Partly that expresses the peculiar demographic and financial fixations of certain newspapers. The same distorting lens has been applied to the imposition of VAT on private school fees. Only about 6% of children attend those schools, but their families are overrepresented in the ranks of Fleet Street editors.

One significant difference between the two policies is that the levy on private education was advertised in Labour’s manifesto, and enjoys public support. Parents wincing at rising bills can’t say they weren’t warned, nor expect sympathy from people who don’t have to pay.

By contrast, Labour’s manifesto only mentioned farming as something to be “supported” and “championed”. Also, inheritance tax is reviled even by those who will be untouched by it. Since only about 4% of estates meet the threshold, that is most people.

Farmers also benefit from a countryside premium when stirring national sentiment. People whose main contact with nature is rambling through it at the weekend or cooking and eating its bounty are easily pricked into anxiety about potential spoilage.

Sentimental attachment to the way things have traditionally been done isn’t necessarily misguided, but nor is it easily kept in economic and political proportion. That is why the fantasy of restoring sovereignty over British fish was a more potent argument in the Brexit campaign than the much more urgent task of keeping supply chains friction-free for less photogenic goods.

Images of tractors trundling down Whitehall and sheep gambolling in fields can distract from what is essentially an argument about fair distribution of pain in an era of hard fiscal choices.

The economics of who can probably afford to pay doesn’t map neatly on to the politics of who can be made to pay. Rachel Reeves encountered this conundrum earlier in the year, when she cut pensioners’ entitlement to winter fuel payment.

That decision dented a lot more bank balances than ending farmers’ inheritance tax exemptions, but there are political similarities. The unwelcome element of surprise is one. No one likes to feel ambushed by the chancellor. Related to that is the reverberation of anger beyond the relatively small group of people who might really suffer to a much wider group that is socially aligned – and still feels targeted.

Many pensioners who can afford to give up their winter fuel payments still resent its confiscation. Farmers whose estates will still be passed on, tax-free, after the changes feel no less solidarity with neighbours and friends whose assets might be worth millions more on paper but who don’t feel rich. Land is not liquidity. Incomes keep shrinking and margins keep tightening.

Pensioners and farmers are also two categories of habitually Tory voter that saw some switching to Labour on 4 July, albeit with narrow-eyed, probationary caution. Their new MPs are now getting letters filled with bitter recrimination and charges of betrayal.

Starmer’s electoral coalition is not so secure that he can afford to make too many sections of it irate. Nor does he enjoy the personal following that means unaffected onlookers will give him much benefit of the doubt when protests are kicking off and accusations of vindictive or bungled exchequer hit jobs are flying.

This is the beginning of a slow-burn political payback for the decision not to seek a mandate for more wide-ranging, universal tax rises (or just to reverse unaffordable Tory tax cuts). That may have been justified as a strategy for winning power, but it leaves Reeves overly reliant on fiddly, precision-targeted revenue raids to balance the books. And each one carries a customised risk of aggravating some sectional interest group with lobbying power disproportionate to the number of people and sums involved.

In these battles, the caveat that “working people” will be spared or that “those with the broadest shoulders should bear the heavier burden” don’t get much traction. Only a weaselly definition of work allows the former pledge to be met, and the latter one is meaningless because breadth of shoulder is a relative metric. Everyone can think of a candidate more suitable than themselves for a higher burden.

The only way to get sustainable consent for the project Starmer and Reeves are undertaking is to hammer home the case for public goods funded by public subscription. There needs to be a rupture from the narrow transactional calculus that frames taxes and benefits as things that industrious people feed into a system for needy (or lazy) people to draw out. Not “I subsidise them”, but “we provide for each other and ourselves”.

Reeves’s budget speech tilted in that direction, but without much emotional heft. Starmer ventured on to this terrain in opposition, when he described the NHS as the “crowd-funded solution for all of us”. But tax-and-spend policy as an instrument of a collaborative national endeavour has not been central to the message.

This is why Labour in government struggles to lift itself out of the defensive crouch adopted for fiscal arguments in opposition. It was hard to shape the terms of debate before winning power. It isn’t easy now. The perfect time to make – and win – this argument would have been before the election. Since that isn’t an option, the second best time is now.

• Rafael Behr is a Guardian columnist