...by making no such foolish mistakes as letting a kid sit in the pilots seat of an airliner moving at 450 knots in unservivable atmosphere and ignoring murphy's law.
Engine failures just happen.
Reversers open in cruise (Lauda Air, Thailand).
Decompressions occur.
What will the commander do at 37.000 feet, standing behind his visitor, unable to take his occupied seat, in such a situation? What will happen to the flight, if the Co has difficulties gaining control, or gets tangled up with his O2-mask, in this very special situation? Different having an empty seat to access then, compared to a kid to be removed first.
Has this to be considered?
By a professional, yes.
Hopefully, no such thing will happen to me in my career. But if so, chances are, I, and hence my company, will get credit by the media if things are run MORE PROFESSIONALLY (see recent Quantas decompression, media response absolutely positive).