I listened to Appiah. He does seem very charming and very insightful. I enjoyed it very much. One thing that exists in the DSM manual to sort out an individual's cultural beliefs from psychiatric delusions is that the belief being asserted by a psychiatric patient should NOT already exist in that person's culture. If a person has grown up with certain prevalent cultural mythologies and beliefs, anything they say based on it should not be construed as being evidence of a psychiatric illness.
It is interesting, for example, to look at the criteria in the DSM manual for diagnosing "Delusional Disorder". I want to draw your attention in particular to criterion #7. :
1.The patient expresses an idea or belief with unusual persistence or force.
2.That idea appears to have an undue influence on the patient's life, and the way of life is often altered to an inexplicable extent.
3.Despite his/her profound conviction, there is often a quality of secretiveness or suspicion when the patient is questioned about it.
4.The individual tends to be humorless and oversensitive, especially about the belief.
5.There is a quality of centrality: no matter how unlikely it is that these strange things are happening to him/her, the patient accepts them relatively unquestioningly.
6.An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility.
7.The belief is, at the least, unlikely, and out of keeping with the patient's social, cultural, and religious background.
8.The patient is emotionally over-invested in the idea and it overwhelms other elements of their psyche.
9.The delusion, if acted out, often leads to behaviors which are abnormal and/or out of character, although perhaps understandable in the light of the delusional beliefs.
10.Individuals who know the patient observe that the belief and behavior are uncharacteristic and alien.
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So what does all this mean to our discussion? Well, simply that in the presence of prevalent cultural delusions, you cannot diagnose individual members of that culture with a mental illness. That's probably because if an idea or story, no matter how dysfunctional, outrageous, or outlandish, is hammered into a child's head repeatedly from the time they are at a tender and impressionable age, then it's going to be no surprise that they will continue to believe that idea when they grow up. But that doesn't make the story or idea any less dysfunctional, outrageous, or outlandish.