The best thing would be if no such illness existed. But, yes, if it is an illness, it would be very good to so determine as therapy methods could then be looked for more easily.
No doubt. As I said previously there is evidence that a "god" center exists in the brain.
Why would you think so?
A convincing explanation would be a long one. One reason that we are susceptible to religious thinking is the way that we infer cause from effect.
Just as we have an innate 'folk physics', we have a folk reasoning.
The specific connection to the placebo effect is that only taste and smell are connected to the hypothalamus, a much older part of the brain. For example, memories associated with taste and smell can last a lifetime, where most visual memories are soon lost.
There is a tendency in children to associate food as being good for them, and this extends to a sort of naive vitalism, that is, they assume that vital power or life force taken from food and water makes humans active, prevents them from being taken ill, and enables them to grow. If true, then the placebo effect would be expected as an inbuilt consequence.
You rightly extol science's achievements, but it is not done by the mind alone.
The scientific method is a tool or prosthetic device that removes as much as possible of our native thinking. Without it, we revert to the native state.
So, your reasoned adherence to atheism (as is mine) is both ours
and the external mental prosthetic devices and libraries of stored information.
Occasionally, some religious minds are converted, and they often ( if not always) speak of the freedom and clarity of thought that it brings. Perhaps then, you may consider it fortunate that you are one of the lucky minority, rather than thinking of the remainder as being idiots ?