Euthanasia supporters are annoyed that it won't become law unless the public says so, despite getting Parliament's approval.
ACT MP David Seymour's End of Life Choice Bill passed its third reading on Wednesday night 69-51 in a conscience vote, meaning MPs didn't have to follow party lines and could vote however they like.
The Greens all voted in favour, along with Seymour (ACT's only MP) and independent Jami-Lee Ross. Most of Labour were in favour and most of National - including leader Simon Bridges - against.
NZ First all voted for the legislation after it was amended to include a clause that it would only become law if a majority of Kiwis vote for it in a referendum, which will be held alongside next year's general election.
Seymour told The AM Show on Thursday it was "partly true" that he thinks the referendum is a waste of time.
"When I first introduced the Bill there was no referendum clause - it was just going to be like any other Bill. In the end, New Zealand First - Winston's got this long-term obsession with referendums, and that was the price of getting their nine votes to make this happen at all."
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But having the referendum come after the law has been passed by Parliament means the public know exactly what they'll be voting on - unlike one particular vote that went horribly wrong.
"This is how the British should have done Brexit. They should have done the deals, passed the law, got it all written down in black-and-white, then asked the British people to have a say."
Matt Vickers, whose wife Lecretia Seales fought hard for euthanasia before her death in 2015, says he wasn't in favour of a referendum either.
"I would have preferred that this was just passed into law last night, nice and simple and neat, but we have to be pragmatic," he told The AM Show.
"There was a good chance if the referendum wasn't included in the Bill, the law wouldn't have passed - and then where would we be? We'd be waiting potentially for another 20 years for a piece of legislation of this character to come up again."
The last time Parliament voted on euthanasia legislation was 16 years ago, when NZ First MP Peter Brown's Death With Dignity Bill was defeated 60-58 at its first reading.
Vickers says the protracted four-year process to get the Bill to this stage has resulted in a "great piece of legislation" his wife would have been proud of.
"She was quite a humble person and I don' think she would have imagined, in her wildest imagination, that things would have gone for so long and for the debate to be so public and for there to be so much of it as there was... I think on the whole she would be quietly proud of the contribution she made to New Zealand in getting the law this far."
Despite the comfortable margin of victory in the House, Vickers expects opponents to put up a well-funded fight against euthanasia ahead of next year's vote.
"The opposition do have quite a few resources behind them to try and dissuade people from voting for this Bill, that is true, and they will try and do that. It's on us... to hold the line and to take comfort in the fact this piece of legislation has been hammered out in Parliament and last night got 69 votes for it.
"It wouldn't have got those votes if this law wasn't safe."
Seymour says the four-year process improved the Bill from his initial submission.
"Everyone knows what they're voting for. Parliament passed the law last night, the public just decide do they actually want it to come into effect."