A True Believer is one who strictly adheres to the tenets of a particular religious doctrine. By extension, one who is strongly attached to a particular belief.
However, the term often refers specifically to the claims made in the 1951 book The True Believer: Thoughts on the Nature of Mass Movements. The book claims regarding "fanatical" "collective" mass movements, that while their stated goals or values differ, such mass movements are claimed to be interchangeable, adherents are claimed to often flip from one movement to another, and the motivations for the mass movements are claimed to be interchangeable. Thus, such religious, nationalist and social movements, whether radical or reactionary, are claimed to attract the same type of followers, are claimed to behave in the same way, and are claimed to use the same tactics and rhetorical tools. As examples, the book often refers to Communism, Fascism, National Socialism, Christianity, Protestantism, and Islam.
Those adhering to such beliefs would likely strongly disagree, citing radically different and incompatible beliefs and behaviors. While such movements may all in some sense be "collective", this also applies any kind of human group having strong common beliefs and goals.
The theory essentially cherry picks, citing some dubious similarities, while ignoring the many dissimilarities.
One example of cherry picking is that, while some people radically change their beliefs, most do not, and most continue to believe the beliefs formed during childhood/youth during the rest of their lives.
Followers are claimed to join because of personal failures and often being poor. This essentially dismisses the importance of ideas and makes an ad hominem attack.
Also, any large mass movement must have support from other groups than only small "elites". Furthermore, for example, Communism has been very influential among students and their teachers at universities, including elite universities. Various state religions have been closely aligned with "elites". Today, fundamentalist Islam and fundamentalist Judaism are supported and funded by very wealthy Islamists and Jews. Fascism was supported openly or tacitly by some "elites" for reasons such as nationalism and anti-Communism.
Another problem with the theory is the implied genetics denialism, with genetics is implied to have no effect on beliefs. See for example the article Political spectrum on stated genetics influences on this.
Yet another problem is that this is a gigantic guilt by association. Any problem by any movement claimed to be a "True Believer" movement can be used criticize any other movement claimed to be a "True Believer" movement.
The theory is similar to the "Horseshoe theory". These theories are often advocated by those seeing themselves as having superior non-"True Believer" beliefs.
Such critics are often supporters of "individualism", such as liberals or libertarians. They may view, for example, critics of the mass immigration as True Believers and a threat to individualism. However, a high degree of support for individualism is associated with White societies and has been argued to have partially genetic causes. This may mean that a high degree of support for classical liberalism may be unlikely among non-White populations and that the support for mass immigration by non-Whites by classical liberals will have the effect of reducing average population support for classical liberalism as Whites become minorities.
- Population Differences in Individualism http://thealternativehypothesis.org/index.php/2016/05/01/population-differences-in-individualism/