while there are the hairy-chested pioneers saying it is fine because they have been doing it for years, the newer pilots in the fold who aren't operating in the extreme conditions accept it as the norm rather than seeing it as a risky thing to do which needs to be justified in terms of safety vs risk.
Wrong!
Every time it was said, it was said at the same time that it must be done "Right".
Which in my version of English connotes being cautious and ensuring it was done in a safe manner. (As the discussion revolves around leaving the Pilot's Seat unoccupied and the Aircraft running at Ground Idle) What we have done as a routine in certain situations over the past Forty Plus Years has proven to be safer than any other segment of flight.
Dig through the Accident Statistics and you will see all sorts of Fatal Accidents.
Why is exercising cautions in this any different than other situations that still result in Fatal Crashes?
We have no idea what really happened in the Grand Canyon accident.
We do not know if the Collective Lock was applied or not.
We don't even know what the main rotor RPM was?
We don't know if the aircraft was setting on uneven ground or a rocky surface.
So with out one bit of real evidence to go on....you wish to condemn a practice that has been done safely countless times.
As two pilot helicopters doing instrument approaches over the water seem to run into the Oggin short of the Deck or Runway......and there always appears to be a CRM issue involved.....what say we go back to Single Pilot IFR and eliminate that source of CFIT Accident? It is the same logic you are using here.