"why he should not have done that?"
Brian Hewitt was the last hole in the cheese. He cannot be held solely responsible for changing the final destination waypoint. Justice Peter Mahon conceded that in his summation of the causal factor of this accident.The safety culture in Air New Zealand regarding Antarctic operations, was severely deficient in situational awareness, crew training and a distinct lack of discipline amongst some crews (management pilots included) regarding flight below MSA. As has been mentioned by many observers during this debate: It was an accident looking to happen.
Have we learnt from it ? Yes we have. Will it change anything? Certainly.