I appreciate its something you’ve spent a great deal of time considering. I may have mentioned I spent seven years as a psychiatry intern so the whole matter of what does and doesn’t constitute a mental disorder was certainly a major them during those years. Having spent the last 12 years in general practice I certainly deal with my fair share of mental disorders. I started to read some of your book. The author is very much coming to terms with religious fundamentalism in America where it affects politics much more than where I live.My opinion that fundamentalism is most likely a disorder is not held for light and transient reasons. I have been weighing the matter for years. For some of my reasoning on this issue, see chapters three and four in Altemeyer's book (linked to in the OP).
One of the major problems with psychiatry disorders is there are no objective tests. It’s all based on what people communicate of themselves and how we experience others. The criteria used by DSM are all sets of symptoms that many of us would experience. Perhaps the most useful criteria is when people’s function affects their work or family life.
There is a definitive exclusion criteria for religious beliefs that are normal for a community. Otherwise whole religious communities become labelled. Then we’ll apply similar criteria to political beliefs. The Moscow school of psychiatry went down that road where political dissidents where diagnosed with this new variant of schizophrenia call sluggish schizophrenia. People were compulsorily detained and treated against their will because the communist state felt threatened. So psychiatry can easily become a tool for social control.
Sluggish schizophrenia - Wikipedia
I don’t like some religious fundamentalists. However, I believe there are much better strategies to counter their negative influences than to label them mentally disordered.