Cargo One
What nonsense! you are equating a scheduled passenger transport flight with a burning building.
I am a Captain with EZ and there is no doubt in my mind that this 'rule' was incorrectly applied in this case. The rule is there to stop crew/ground staff attempting to ask others to care for a child during a flight. If a parent does it, that's now the parent's issue and no longer the concern of the airline.
If I had been asked to rule on the circumstances on that day, having clarified that the parent was happy - close doors and go!
Not worth 4 pages of PPrune though...........