Permitting mercy-killing of people with terminal illnesses would inevitably lead to the killing of newborns with disabilities and the elderly, an anti-euthanasia campaigner says.
The head of the Canada-based Euthanasia Prevention Coalition, Alex Schadenberg, will speak in Auckland on Saturday at a conference organised by the Euthanasia Debate group.
He arrives as Labour MP Maryan Street prepares to put her assisted-suicide bill in the ballot for private members' bills.
"It allows people who have a terminal illness or who are suffering from an irrecoverable condition to determine how and when they wish to die," she said.
"It's not just for terminal illness. It is also for those who have a condition where their quality of life is so diminished they don't want to live any longer."
In the Netherlands, doctors are permitted, under strict conditions and at a patient's request, to end the person's life or assist their suicide.
Mr Schadenberg, speaking from Adelaide yesterday, said that if New Zealand followed suit, the permissible grounds would gradually widen.
He cited the Dutch permission for killing severely disabled newborns and a campaign - resisted by a majority in the Parliament - to allow euthanasia for people over 70 who were "tired of life".
Under Dutch law, doctors can perform euthanasia if the patient is in unbearable suffering from a medical condition and has no prospect of improvement.
The Netherlands physicians federation says non-medical factors such as "loss of function, loneliness and loss of autonomy" can be part of the evaluation of suffering, and that the law can apply to patients with psychiatric conditions or dementia.
Dutch paediatricians writing in a leading US medical journal in 2005 described the legal protocol under which euthanasia of newborns, typically those with severe forms of spina bifida, can be permitted.
"When both the parents and the physicians are convinced that there is an extremely poor prognosis, they may concur that death would be more humane than continued life."
Mr Schadenberg, who has a disabled son, said such killing of newborns for what was deemed to be unremitting suffering amounted to "quite a eugenic ideology. It was not on the table at the start of the Netherlands' euthanasia."
Ms Street said her bill stood a good chance of success because the social balance had moved more in favour of voluntary euthanasia since the Death with Dignity Bill was defeated in 2003 by 60 votes to 58, with one abstention.
Her bill's protections would include requiring two medical practitioners to attest to the patient's condition and that the person was of sound mind at the time of making the request.
The bill would provide for end-of-life requests to be made in advance. It would also provide protection against people being coerced into requesting death.