"Do you really believe that Air NZ is totally clear of blame in regard to this tragedy?"
As stated many times, no.
"Do you really believe that Air NZ had considered every possibility of risk mitigation before authorising Antarctic flights?"
They never had the final say on approving these flights, CAA had that responsibility, they laid down the requirements for descent. It was because CAA were very lax in policing these requirements that they got their wrists smacked, in fact there was an airline inspector scheduled to go on that flight, because of a family illness he had to cancel. I would find it hard to believe that the flight would have been carried out the way it was if that inspector had of been onboard.