The Universal Basic Income is touted as a way to ensure dignity, tackle poverty and reform the welfare state. Its opponents argue it’s too expensive and too simple for a complex world.

The core idea is that every citizen, regardless of income, gets a basic payment from the state. This is often paid for (in theory) by a flat rate income tax and/or a wealth tax. Indeed most arguments for a basic income stress the need to see benefits and taxes as part of one system, and the basic income can be seen as a kind of tax rebate.

The advantage of a basic income is that it would give everyone some security of income, and would recognise that, as a measure of their basic human worth, everyone is entitled to some income, regardless of what they are doing with their lives. The model here is National Superannuation, which is paid to everyone over 65 regardless of their status.

A basic income would remove some of the complexity of the current means-tested welfare system, reduce stigma, recognise the contributions of people doing unpaid work (notably child-rearing and voluntary activities), and help protect against the instability of precarious jobs. Because it would not be taken away if people earned more, it would not act as a disincentive to finding work, as traditional benefits do.

The basic income has advocates across the political spectrum, including high-profile libertarians such as the US author Charles Murray, and is being contemplated or trialled in countries including Finland, the Netherlands and Canada.

The arguments against the basic income fall into two, related camps. The first is simply the expense, which relates to the level at which the basic income is set.

One common argument is that the basic income will always be too generous to be affordable or too low to make a difference to people’s lives. If the basic income is to ensure that everyone relying on it can lead lives of some dignity and security, and can stay out of poverty, it would need to be at least $18,000. (The least demanding poverty line is that people need to have more than half average disposable income, which is $36,000.) Paying that to 3.5 million adults would cost $63 billion, reduced perhaps to $46 billion once savings from the existing welfare system are counted – a very large amount in a country where spending on all the government’s core issues (core Crown expenditure) in 2016-17 is planned to be just $78 billion.

In contrast, the basic income is often modelled at a lower level, around $11,000 a year, roughly the rate of the unemployment benefit. That still costs $38 billion, slightly reduced once savings from the existing welfare bill are counted. And at that level the basic income – which many people unable to gain paid work would rely on – would be insufficient to allow people decent lives.

The second argument is that the basic income is too simple a solution to a complex world. The reason that the welfare system is so complex is that life is complex. People with disabilities need more support than those without; people in Auckland face different costs from those in the regions; and so on.

New Zealand’s current benefits range from $11,000 a year (the dole) to $18,000-19,000 a year (Superannuation). Any basic income that tries to replace the welfare system will, unless set very generously, leave some groups – such as sole parents – worse off.

One possible compromise is to advocate the basic income as one part of the welfare system – a universal core on top of which other benefits are paid – rather than a complete replacement. Arguments about the basic income may also be modified in future if – as some argue, though it is far from certain – automation leads to widespread and irreversible unemployment. Then, it is claimed, a basic income, paid for by a wealth tax on robot owners, would be essential.