If the system had 'the pertinent sentence' continue with the words, "until the rotors have stopped", at least one life may have been saved; and it's future amendment may save others in the future. Having said that, just because you are allowed to do something, doesn't mean you have to!
"If" is the magic word.
Because you
are allowed to do something, it means you may.
The question of Risk Management is an all together discussion than what we have focused upon lately in this thread.
Yes there is Risk to "leaving the flight controls un-attended", no question that there is. The real question is if it is going to be done, how best to do it to "minimize" the Risk. That would include a choice of situations, choice of aircraft, choice of best method to prevent problems.
One could even skip over all the analyses and study and merely ban the procedure and eliminate those risks. The question that should follow that is if you increase risks of other problems by restricting the Pilot to the Cockpit if you do a Turn Around with Rotors Turning and you have passengers or Loadies loading and unloading the aircraft and boarding or exiting the helicopter where the Pilot cannot control the situation or see what is going on at the other side of the aircraft?
Do you then ban all such activities until the engines and rotors have stopped which would be the safest situation possible? After all if one is concerned in reducing Risk then why take any chances whatsoever?
How far do you go in writing Rules and Regulations to minimize Risk before you make it impossible for people and companies to operate helicopters?
It must get back to determining the level of risk one is willing to accept after rationally examining the practice under consideration.