Interesting perspective
Passenger spots contamination on wing ..crew decides that its irrelevant despite it being illegal!
Back to the Munich disaster where it got three inquires to exonerate the crew. Yes I know it was slush but the similarity is that it is venturing into the unknown.
But once the doors are closed the captain's word is law which doesnt mean he can get away with it especially if it is reported.
If I had doubts whether lhs or rhs I would go back with a torch and check the wings regardless.
Wasnt there an aircraft that ended up in the Pontiac?