Calling pax 'silly' and SLF does not help the matter one little bit..
What would you do in the case of a knowledgable pax informing you (via the cabin) crew that the slats/flaps were not deployed for take off - call him silly and ignore it?
The derogatory term SLF does not take into account that some of the pax could be 1/. Staff, with at least your knowledge 2/. Frequent travellers who may themselves be private pilots, or, any other combination.
You can go back to the Trident disaster at Staines to find that the slats/flaps (slats or droops in that case) and their deployment or not have caused many deaths(LH 747 at Nairobi?) - and yet it is still happening.
Complacent attitudes do not help the matter.