ALthough some rules seem arbitrary, I think many are instituted in order to formally "draw the line" somewhere.
As mentioned earlier, if we leave it up to individuals to make field judgments regarding certain situations, there is an infinite range of interpretations, and rationalization.
Just for fun...
Of the guys who see no problem with installing minis in a 40 ckt. panel, how many would you be willing to install?
(No condescension, or patronization intended, just a social experiment. [Linked Image])