Dutch Professor Dr Theo Boer says euthanasia laws can alter the "whole fabric of society".
Once a euthanasia supporter, Dr Theo Boer appeared on TVNZ1's Q+A talking about his experience reviewing euthanasia cases in the Netherlands.
In New Zealand on a trip paid for a lobby group against euthanasia, he told host Jack Tame he initially "had the impression it was a good system (in the Netherlands), it was reliable and it kept the number down to an acceptable level".
However, he said a few years after he was on the euthanasia review panel in 2005, the number of cases began to rise.
"Not only that, the reasons why people wanted to have euthanasia expanded rather dramatically from terminal illness towards psychiatry towards people with dementia, with chronic illnesses. It gave me feelings of discomfort.
"I think there is a right of every person to decide to die, but I don't know if there's an obligation or a norm from the Government to make sure this person can die.
"What I see is that a euthanasia law may do something to the whole fabric of society... the availability of euthanasia has changed the whole way we see dying and suffering."
ACT's David Seymour said it was important to look at the other euthanasia laws around the world.
"We've had a very robust debate here in New Zealand. It started most recently with the Lecretia Seales case in 2015, I've been up and down the country debating this, it's had the longest Parliamentary process of any bill in Parliament I can think of.
"We've come to a pretty settled place where Parliament and the public seem at this point... to be happy with the bill that is for people suffering at the end of their life, people who are terminal."
New Zealand's proposed euthanasia law is currently going through Parliament.
Q+A is on TVNZ1 on Mondays at 9.30pm, and the episode is then available on TVNZ OnDemand and as a podcast in all the usual places.