Heretics were routinely burned alive just a few centuries ago. Or stoned to death, or executed by whatever method local fashion demands. Questioning the local gods is the notional crime for which Socrates was made to drink hemlock.
These pressures would also strongly select for cheats who simulate faith without having the real thing, leading to a religious form of Batesian mimicry.
So, if you are an emperor wanting honest advice on your wardrobe, then Asch's results suggest that 'planting' one or more dissenters would be a good way to get it.