Former prime minister Sir Bill English has urged MPs to reject a bill legalising euthanasia saying such a move would be a "slippery slope".
English is one of two high-profile Kiwis on opposing sides of the debate who will make submissions to a select committee considering the End of Life Choice Bill today.
Matt Vickers, the husband of Lecretia Seales, is also making a submission to the Justice Select Committee.
English and his wife Lady Mary told MPs that killing had always been banned and that was fundamental to humanity. This bill would "ask us to look the other way".
What started as permitted would become desirable and then for some then an unconsented necessity, English said.
"That is the slippery slope," he said.
Usually, legislature works very hard to mitigate what would be very small risks - this
would open large risks, he said.
"Safeguards mean nothing if there are no consequences."
English said the test for consent was poor in the proposed Bill and did not meet the necessary threshold.
"You have to make sure no person had their life taken against their will … that's the threshold."
English said the conscientious objection clause did not protect doctors who oppose euthanasia and that was "repugnant".
"The impact on the common good is much greater" than proponents would accept.
Husband continues fight for assisted dying
Lecretia Seales, a Wellington lawyer, was diagnosed with terminal brain cancer in 2011 and campaigned for the right to end her own life with the assistance of a doctor.
In May 2015, she took a case to the High Court of New Zealand seeking a judgment that would protect her doctor from prosecution should she consent to die with medical assistance.
As her health deteriorated, her aggressive brain tumour caused gradual paralysis and she lost her eyesight on her left side.
Seales died on June 5 2015, on the same day the judgment in Seales v Attorney General was delivered.
Justice David Collins ruled that a doctor could not assist her to end her life without the risk of prosecution.
The End of Life Choice Bill, sponsored by Act Party leader David Seymour, has received a record 35,000 public submissions to the Justice Select Committee.
This is the most submissions received by a select committee since the legalisation of same-sex marriage drew 22,000 submissions in 2012.
The proposed law change would give people with a terminal illness or a grievous and irremediable medical condition the option of "requesting assisted dying".
"The motivation for this bill is compassion," it says.
"It allows people who so choose, and are eligible under this bill, to end their lives in peace and dignity, surrounded by loved ones."
Former PM a staunch opponent
English staunchly opposes euthanasia and his written submission says the End of Life Choice Bill was bad legislation.
Parliament regularly limited freedoms in order to reduce the possibility of death or injury or inconvenience but in his experience Parliament never legislated to increase the possibility of death, even with safeguards, his submission said.
"The legislation is based on personal autonomy and the right of individuals to choose euthanasia.
"Yet the legislation limits eligibility to some health conditions which a third party
can identify as potentially a cause of excessive suffering."
English said the conscientious objection clause did not protect doctors who oppose euthanasia.
"Doctors who oppose euthanasia are obliged by this legislation to refer a person
requesting euthanasia to a doctor who is certified as willing and able to assess and euthanise a person.
"There is therefore no practical difference in what happens to a patient between attending a doctor who opposes and a doctor who supports euthanasia. The conscientious objection clause is a sham because no doctor can choose not to participate."
English's wife Lady Mary English, who also opposes euthanasia, will also speak to the committee today. The couple are both practising Catholics.
In his written submission to the Justice Select Committee, Matt Vickers said his wife was a confident, intelligent woman who loved her life and did not want to die.
"But she was also pragmatic, and when she realised her death was inevitable, she sought to make it as bearable for herself and for others as possible.
"For her, that meant being surrounded by family, having good palliative care, and remaining as lucid as possible.
"But it also meant being able to say goodbye at a time of her choosing, and in a manner of her choosing. She felt that being denied that choice was a denial of her humanity."
Vickers reviewed the End of Choice Bill alongside the lawyers who had advocated for his wife and said he believed the safeguards in the bill were "rigorous and comprehensive".
Vickers has organised for a memorial lecture to be held this evening at the Old Government Buildings in Wellington.
The lecture will be led by Julian Gardner and Tricia Malowney who have travelled from Australia to attend the event.
Gardner is a lawyer and immediate past Victorian Public Advocate. Malowney is a health advocate for women with disabilities and was the Inaugural President of the Victorian Disability Services Board.
"It's pretty special to get not one but two experts from the Victorian inquiry visiting New Zealand - these folks have examined the issue from all angles and will likely be the most informed individuals that the New Zealand public and MPs will have the opportunity to hear from," Vickers said.