Everyone hates GST, according to Prime Minister Jacinda Ardern.

She made the remark in jest at a powhiri at Waitangi in response to an equally jocular request for GST exemptions from some on the paepae.

"Everyone hates GST," she said, "except maybe Grant Robertson".

She's probably not wrong. John Mitchell, a man with a rare cancer, recently speculated the Government was raking in millions in GST on unfunded cancer medication.

Mitchell noticed this when paying for two months of cancer medication recently. He saw the GST component on his $14,800 bill was $1900.

GST is a much unloved tax, mainly because in New Zealand it taxes everything. This has led to calls for things to be exempted from it.

The Labour Party previously campaigned on exempting fresh fruit and vegetables. It even embarked on an "Axe the Tax" tour, driving a big red bus around the country protesting the Key Government's plans to hike GST to 15 per cent.

They're all worthy goals. It's a tragedy in New Zealand how many essential medicines are still prohibitively costly, likewise fruit, vegetables and other life essentials could always be cheaper.

But the reason why these campaigns are unsuccessful is the reason why Robertson, according to his Prime Minister, is the only kiwi who doesn't hate GST: it brings in a lot of money.

SUPPLIED Opposition Leader Phil Goff and Labour MPs once held an "Axe the Tax" bus tour to rally against John Key's plans to hike GST to 15%.

According to IRD's 2019 annual report, it netted $19.4 billion last financial year, a quarter of all tax revenue.

To put that in perspective, it's roughly the size of the entire health budget.

GST in New Zealand is special. We're one of the only countries in the world that doesn't exempt things from GST, no matter how worthy. That means it brings in a lot of tax. New Zealanders pay more consumption tax (the category of tax that encompasses GST) as a percentage of GDP than any other OECD economy.

The simplicity of the tax is its greatest strength, making it very difficult to avoid. David Lange, whose Government introduced GST quipped it was so effective, even drug dealers paid it.

Despite its apparent unpopularity, the tax has some defenders.

Robyn Walker, a tax partner at Deloitte calls it an "ideal tax".

"The fact there aren't any exemptions makes it an ideal tax. It makes it perfect to comply with you and don't get uncertainty, compliance costs and advisors costs that you get in Australia," she said.

Robin Oliver, director of Oliver Shaw tax advisors agrees.

Ross Giblin Higher GST doesn't always mean higher prices.

"The key feature of our GST is it's a single rate and that we should keep that because once you move away from what we've got which is single rate and you have exemptions or different rates you've lost," he said.

He warned of unintended consequences, for example exempting GST from food and vegetables. While it may sound good in theory, potentially encouraging people to pick healthier groceries, it's complicated to implement.

Would an exemption apply to restaurant food? There's a good chance it may, in which case the tax would be a subsidy to wealthy restaurant-goers as much as it was to struggling families.

Then there are problems of definition. In the UK, for example, VAT (a European equivalent to GST) was levied at different rates on hot and cold food until 2012. The products were the same, but the tax rate differed depending on how warm it was.

Most of the arguments made for exempting GST highlight the fact it would make certain essential goods cheaper, but Walker isn't so sure.

"If you do exempt something that's not to say the benefit of that GST will get to the end consumer," Walker said.

"It can sit as a tax cut to the vendor," she said.

In this case, people looking for cheaper goods will be out of pocket twice. The things they want will still be expensive, but the state will have less money at its disposal to potentially use as a government subsidy.

Both Walker and Oliver agree that if the Government wants to boost people's incomes or reduce the cost of things it would be more effective to use the transfers system: thinks like Working for Families, or subsidising expensive things directly.

"If it comes down to something like cancer treatment, Oliver said, "Is there something more targeted? Is there some sort of rebate, outside of GST?"

Endless GST exemptions just undermine the integrity of the system, ultimately meaning there's less tax that can be used to help boost people's incomes or subsidise the expensive things they need.