A Christian telling an atheist they're going to hell is as scary as a child telling an adult they're not getting any presents from Santa.
What happens to the faith healer and the shaman when any poor citizen can see the full effect of drugs or surgeries, administered without ceremonies or mystifications? Roughly the same thing as happens to the rainmaker when the climatologist turns up, or to the diviner from the heavens when schoolteachers get hold of elementary telescopes.