In the wake of the decision to scrap the proposed mega-prison at Waikeria, the 'get tough' brigade are banging the law and order drum. They say putting record numbers of New Zealanders in prison has made the country safer. They are wrong.

Crime rates have been falling for 30 years, not only in New Zealand, but throughout the English-speaking countries and Western Europe. The trend has nothing to do with imprisonment. Crime fell in America, which built the largest prison system in the world, but also in Finland and the Netherlands, where imprisonment was cut considerably.

America debunks the assumption that more prisons means less crime. Crime is falling most dramatically in states that are reforming and lowering prison numbers, as Labour is proposing here. Vermont cut the prison population almost a quarter between 2010 and 2015 and crime dropped a third. In New Jersey, incarceration and crime both fell 20 per cent.

Garth McVicar says prisons keep us safe by locking away the "bad buggers." But they are an ambulance at the bottom of a cliff, the intervention comes too late, when the police arrive the damage has already been done. And the prisoner eventually gets released, often deeply scarred by the experience and more dangerous than before.

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More importantly, the "bad bugger" has probably been homeless and suffers with untreated addiction and mental health problems. They likely come from a community with many police and few living wage jobs. Our massive investment in prisons has been coupled with systemic under-investment in the social supports that prevent violence.

The real question for policymakers is not whether prison works, but whether it is the best possible way to spend scarce resources.

Lets take a healthcare analogy. Suppose we live in a society that tolerates abysmal sanitation, and because of this, suffers predictably high levels of preventable disease. Under these conditions we will "need" to build a lot of hospitals to care for the sick and keep them away from others – which the hospitals will to some extent do, and therefore "work." Yet people will still be getting sick from a lack of prevention.

So it is with violence. If we accept the conditions that predictably breed large amounts of violent crime – record levels of inequality, for example, or broken mental health systems – then we will "need" a lot of prisons. Building more may even prevent some crime. But the approach will still be irrational because there are far better alternatives.

New Zealand is in the middle of a housing crisis. We have built six prisons since 2005, some the size of small towns. On current forecasts, we will need another every three years. The Government is scrambling for resources and construction capacity to build affordable homes. I hope they will ignore the tired get tough slogans from National and Garth McVicar. Building houses will work far better, making our people safe, than building prisons.

We should start with an honest assessment of the evidence. From there, policy choices become a question of values about the kind of society we want New Zealand to be. Houses not cages wins on that count too.

Liam Martin, criminologist at the University of Victoria.