"It is clearly established that, when the pilot told Mac Centre he wished to descend VMC, he effectively informed the controllers that he could see where he was going. In so doing, he took sole responsibility for separating the airplane from other aircraft and the terrain, and he was on his own."
They approved his request for a VMC descent, as they had never identified him on radar, and had no means of knowing what the position of the aircraft how could they give them a clearance to descend????
" he took sole responsibility for separating the airplane from other aircraft and the terrain, and he was on his own."
This is what they requested, a VMC descent, MacCentre approved a VMC descent.
"ATC did give a clearance to descend to 2,000 ft VMC and proceed visually to McMurdo."
All they were doing, as the captain had assumed responsibility for his own terrain clearance and separation from other aircraft, with his request for VMC descent, was advising him of no known conflicting traffic.
It is patently obvious that Mahon had no understanding of, and obviously got no accurate advice on, the meaning of a VMC descent. The controller had no way of knowing the position of the aircraft, or the weather it was encountering, the captain had by requesting VMC descent taken on all responsibility for terrain clearance and separation from other aircraft upon himself, in complete disregard of the mandatory requirements for descent.
Surely the end result speaks of the folly of this decision.