More than half of the people who had their visas cancelled in Australia between 2014 and March, 2016, for having spent time in prison were New Zealanders.

OPINION: Australia's aggressive trawl to find foreigners on its soil with a criminal history, so it can boot them out, is well-known by now.

From the start of 2014 to March last year, 697 New Zealanders were swept up in it, with many sent to languish in remote detention centres. More will have been found since.

There is no mystery about why Australia has done this; it is a mere extension of its often brutal immigration policy. It is also, as the Labour MP Kelvin Davis puts it, "political gold". No government ever lost support by attacking criminals, let alone those from overseas.

Still, new reports from the country's immigration watchdog, the Commonwealth Ombudsman, are one more spotlight on a shameful system.

They show how the policy separates people from their families, sometimes after they arrived in Australia decades ago.

One New Zealand man, for instance, arrived as a six-year-old and was convicted of theft as an adult. He was sentenced to 12 months in prison and served two months. When the Ombudsman's office spoke to him, he was waiting in a Queensland detention facility, separated from his partner and children, who cannot afford to follow him if he is sent to New Zealand.

Such stories add to those of other New Zealanders already made public – that of Junior Togatuki, who arrived in Australia as a four-year-old but who died in solitary confinement in Sydney in 2015 as he waited to be deported; or that of ex-soldier Ko Haapu, held for months merely for being associated with an outlawed motorcycle club, a good example of Australia's extremely wide provisions for detention.

The Ombudsman also shows that the process is painfully slow. Many people only find out their visas have been cancelled at the end of their prison terms – ensuring further stays at crowded detention centres as they plead for a waiver. That is effectively a second spell of imprisonment.

Finally, the report confirms the special place for New Zealanders in the Australian trawl – they made up more than half of all of those who had their visas cancelled. So much for Anzac spirit.

Of course, the Australian government says it will not apologise for a policy that "protects the Australian community". This sort of tough talk reflects the idea that countries should be able to banish anyone who doesn't have citizenship, for nearly any reason.

Just as reductive is the idea that all the deportees are "murderers and rapists", to quote former Prime Minister John Key, and thus deserving of scant sympathy, however they are treated. That is cruel and unfortunate. Most have committed less serious crimes than that, some far less so.

And nationalism doesn't really wash when Australia is prepared to host Kiwis for nearly their entire lives, without the prospect of gaining citizenship, only to ditch them if they cause trouble.

It was absurd when, in 2009, Australia sent Patricia Toia back to New Zealand, even though she had crossed the Tasman as a one-year-old and committed all her crimes in that country. And it is sad and harsh too that it is expelling hundreds of people now, to a "home" country many hardly know.