Taxing the rich to give to the poor – who could possibly object? The average person surely wants to see another 20,000 children lifted out of poverty, and will therefore support Humza Yousaf’s plan to introduce an additional tax band in the next Scottish budget. Isn’t it a no-brainer?

Well, that depends on a few factors. The first is who we consider “rich”. The second is whether raising income tax will actually deliver the increased revenue required to achieve the policy’s aim. The third is whether creating further income-tax divergence within the UK will have negative long-term consequences.

The richest, of course, don’t have to worry about personal income tax.

They aren’t rich because they work longer hours than the rest of us, or put in the same shifts but on a higher hourly wage. Some of them need not work a day in their lives, thanks to inherited wealth. Others may run their own businesses and pay themselves a minimal salary to keep their income tax liability at zero.

Yousaf spoke during the leadership contest about introducing wealth taxes if he were to become First Minister, so we’ll return to that shortly, but for now, let’s focus on employees who are taxed on a “pay as you earn” (PAYE) basis.

READ MORE: Humza Yousaf to back wealth tax if made first minister

Which workers are the “rich” ones who can afford to pay a bit more to help those with the least? Perhaps the image that comes to mind is of a bonus-enriched banker or corporate lawyer, or those in the kind of cushy business consultancy roles that await many former politicians.

But income tax changes don’t discriminate between essential and non-essential workers, hard-working professionals and chilled-out-executives. Do we feel differently about higher taxes for a specialist doctor working long hours in an overstretched hospital? A principal teacher working to inspire pupils in a school in a deprived area?

The struggle to recruit staff for Scotland’s NHS has been well-documented, with figures emerging last year that suggested there were more than 9000 consultant vacancies in the country, equal to 14% of the senior doctor workforce. This figure was obtained in response to a freedom of information request from the British Medical Association, which claimed it provided a more accurate picture of the crisis than the 6% shortage claimed by NHS Education Scotland.

Whichever percentage is considered the more accurate, where does pledging to increase income tax for some of those earning between £43,662 and £125,140 a year fit into a recruitment strategy that until recently was Yousaf’s specific responsibility?

The Institute for Public Policy Research (IPPR), which has welcomed the new FM’s proposal of a new tax band, has modelled a new rate of 45% for those who earn above £58,285. This is described as representing “just a three-percentage-point increase on their current rate”.

READ MORE: New tax band could help 20,000 children escape poverty

The think tank declined to set out why a highly skilled and experienced foreign doctor earning £60,000 or more would be specifically attracted to work in Scotland and pay the additional tax, given NHS England is facing a similar recruitment crisis.

Perhaps asking such a question is considered to be “talking Scotland down” by those in the Scottish Government, who might point to some of the universal benefits available to those living north of the Border. The question is, how many of these would be of relevance to a high-earning professional pondering relocation? Free prescriptions? Free university education for any dependents choosing to stay here to study?

An alternative stance may be that high-earning professionals will seek to live in a country where well-funded public services benefit all, creating a happy, healthy society.

But Yousaf has pledged to spend the additional tax revenue not on public services but on increasing the Scottish Child Payment by £5.

READ more: Humza Yousaf must be careful over pressure on 'progressive agenda'

The IPPR may have crunched the numbers based on Scotland’s current tax base, but what if over time the tax base changes, and those earning more – or simply aspiring to earn more – were to leave? Given our lack of power over immigration, how would we make up the income tax revenue shortfall? When quizzed by Kate Forbes on his plan to expand the tax base, Yousaf’s reply was limited to his pledge to fund childcare so that mothers could return to work sooner.

The National: Humza Yousaf pitched himself as the 'progressive candidate' during the leadership election and his tax plans are a continuation of thisHumza Yousaf pitched himself as the 'progressive candidate' during the leadership election and his tax plans are a continuation of this

Towards the end of the leadership campaign, when asked about the possibility of taxing wealth – such as via a land value tax on big estates – Yousaf said he would go in “with a really open mind about how we can use our devolved powers to maximum effect.” Is his mind open to finally scrapping council tax?

And could it be opened further, amid the ongoing Fiscal Framework Review, to pursue additional powers for the Scottish Parliament that might allow for more radical – and fairer – approaches to taxation?

Perhaps making high earners pay more will prove to be the more politically appealing option, at least to those voters who aren’t high earners themselves.

But if such a voter later ends up in a hospital where doctors are in short supply, they may wish other options had been considered.