Tourism businesses didn't have the expertise to make sure trips to Whakaari were safe - and scientists should have been in charge, a leading geologist says in his opinion.
However, a pilot who rescued seriously injured victims from the volcano says tourist operators did everything they could to keep people safe.
Nineteen tourists and two guides were killed after being engulfed in a pyroclastic surge on the volcano's crater, on December 9 last year.
The alert level for Whakaari / White Island had been raised to 2 three weeks before.
This month, NZME revealed tourists would not have been allowed on Whakaari at alert level 2, under Department of Conservation's volcanic safety protocols.
But they weren't in place because Whakaari / White Island is privately owned, not overseen by DoC.
In April 2016, the island erupted overnight when nobody was there.
GNS scientists later said anyone on the crater would have had a low likelihood of survival.
Melbourne-based Monash University Emeritus Professor Ray Cas told NZME he believed this should have been a "trigger" for "totally reviewing" tourist visits.
In his opinion, volcanologists and risk scientists "should have the overarching right to make decisions on what is safe and what is not" on volcanoes as active as Whakaari.
However, Kāhu NZ chief executive Mark Law, who immediately flew to the island to rescue the injured after last year's explosion, rejected Cas' comments.
In Law's opinion, Cas was "passing the buck and blaming".
He said "GNS did a great job" of sharing information "and we used this to the best we could".
"We always took it seriously."
Law said tourist businesses such as his balanced "generating incomes, supporting the community, paying taxes, [and] providing our visitors with the best experiences we can safely".
"We did everything we could to do to navigate the risk associated with a live volcano."
University of Canterbury's Professor Tom Wilson, who specialises in disaster risk, told NZME giving scientists control of tourist access to volcanoes "would be a major change and potentially create new issues" in New Zealand.
"So this would need to be considered as part of the wider system of assessing and managing volcanic risk," he said.
"The key point is that we want the best expertise available ... so that the best possible decisions can be made. This should ideally be scientifically-based, impartial and transparent."
Auckland University of Technology's Professor Michael Lueck, who specialises in tourism, said New Zealand needed a "nationwide system for safety" to oversee adventure tourism on volcanoes.
He said certain levels of activity noted by GNS and volcanologists should "automatically" stop visits.
In Lueck's view, adventure businesses also needed to better inform tourists of risks.
"This has to be done in an easily accessible and obvious way."
If tours return to Whakaari, they should only go at Level 1 or below, he said.
But Cas believed tour groups shouldn't go back on to the crater at all because there was no way of guaranteeing anyone's safety on "the most unpredictable, explosive volcano in New Zealand".
"It's very dangerous to take tourists to Whakaari at any time ... It is basically, eventually, asking for trouble."
For the past 30 years, tourism businesses have made their own calls about when to visit the island or not.
Earlier this year, NZME reported there were seven life-threatening "near misses" at Whakaari in the years leading up to December's devastating eruption.
In February this year, NZME requested copies of any GNS documents where staff had recommended tours to White Island / Whakaari be halted, since 2016, under the Official Information Act.
But there were none because such recommendations are outside GNS' mandate.
GNS declined to comment and other Whakaari tourism operators approached by NZME did not respond to requests for comment.