Well at the risk of causing further upset, lets recap and see what we appear to be facts:
Oiling your fretboard can make it look and feel more pleasant.
Over oiling can cause problems by softening the fretboard.
Oiling varnished fretboards can cause unpleasant streaking.
Then some points which are matters of opinion, but less contentious:
Sellers of fretboard oil emphasise the benefits of their products to help drive sales, which may encourage over-use.
Significant damage is rare and moderate use of fretboard oil doesn't seem to cause problems.
Custom fingerboard oil isn't significantly different in performance or effects, but smells more pleasant.
My personal opinion:
More instruments are ruined through over adjustment of truss rods and clumsy customisation; no-one is going to say 'stop adjusting your truss rod' or 'don't fit new pickups'.