By religious fundamentalism I mean any system of belief that thinks the truth to be the literal reading of a text revealed by an omniscient being.
By irrational I mean being not being based upon reason, and even more specifically - contrary to reason
The transcendental argument for the existence of God, which arguably originated in the presuppositional apologetics of Cornelius Van Til, would have us believe that if God did not exist, or more specifically if Christian scripture as a whole is not presupposed to be true, then no metaphysical or epistemological identifications or distinctions would rationally be possible at all. Although absurd (and perhaps evil, in the end), the argument isn't quite contrary to reason, after all.
Note that I say "arguably originated": it is possible to interpret Descartes as advancing something like this style of argument. As the linked article quotes Descartes:
[O]nce we have become aware that God exists it is necessary for us to imagine that he is a deceiver if we wish to cast doubt on what we clearly and distinctly perceive. And since it is impossible to imagine that he is a deceiver, whatever we clearly and distinctly perceive must be completely accepted as true and certain.
Another option (in the same broad tradition, though) is Reformed epistemology. This is the idea that belief in God is warranted by virtue of being properly basic, in line with belief in experience or mathematics being warranted by virtue of being properly basic. In one form, this theory involves something known as the sensus deitas or sensus divinitatis, which is effectively equivalent to a "sensation" of the Creator's reality. This theory can go on to include the epistemic action of the Holy Spirit as granting warrant to beliefs, e.g. specifically belief in Christian scripture.
Now, let us suppose that the law of noncontradiction is correct. Let us more exactly suppose that it is correct because otherwise we would run afoul of the principle of logical explosion. Then suppose that some or all scriptures (various compilations and translations of the Bible, the Quran, etc.) are inconsistent. Per the explosion principle, the inconsistency of these texts would allow us to infer anything whatsoever from them, e.g. that God does and does not exist, is and is not a yellow anteater, will and will not forgive sins, and so on and on. One suspects, then, that if these texts are inconsistent, it is irrational to believe in them. In fact, we could say: since every proposition whatsoever can be inferred from their inconsistency, then so can the individual proposition, "It is irrational to believe in these scriptures," be inferred from these scriptures as such.
You might find this discussion relevant. "What is a Trauma Bond with God" https://www.youtube.com/watch?v=Ft_6sNhHuoU She explains the difference between having a positive and a negative relationship with God and how some religious communities foster negative relationships with God, i.e. trauma bonds with God, in order to control individuals.
Not necessarily. It depends on your theory of rationality (that is, on what counts as contrary to reason).
A minimal account of rational belief is: A belief state is rational iff it is logically consistent (doesn't entail a contradiction).
Now, it's possible for there to exist a logically consistent text that purports to be divinely revealed. (For example, perhaps the text is just "God revealed to his prophet, Moses, that he created the universe.")
So, it's possible to be a rational fundamentalist according to the minimal account of rationality.
(Few people accept the minimal account, but most people accept that logical consistency is at least necessary for rationality, which is why a lot of attacks on fundamentalists try to show that religious texts contain claims that, when taken literally, are inconsistent.)
There is no rational process that can lead us to the conclusion that a set of scriptures (any scriptures, in order to not single out a specific religion) is a text revealed by an omniscient being, baring the immediate knowledge of this being, including a convincing demonstration of its omniscience (but then, we wouldn't need the scriptures in the first place...)
Putting aside all the flaws and contradictions that can be usually found in scriptures, the inadequacy of their content with scientific knowledge that is demonstrated to work, the historical knowledge we have of their authors and how their theology usually appears to be informed by the issues of their time and culture, all of which cast more than a reasonable doubt of the divine nature of the authorship.
How do we rationally establish that an author is omniscient based solely on their work ? By finding true statements in the book ? But being right about a finite number of verified statements is no sufficient proof for omniscience. A lot of true statement in a work can grant credibility, but credibility is not omniscience: I tend to believe my doctor because they gave me good advice so far, but they might still be wrong one day.
Even if the true statements are remarkable, far from mundane, for example very specific prophecies that came to pass, or facts that couldn't be known at the time of publication, and even if we take the claims at face value, it only means the author had access to this specific information. They could be time travellers, pixies or aliens, all of whom might know a lot but are not omniscient.
Let's say we have identified an actual omniscient being that we are cognizant of by using one of the many claimed argument for god (ontological, presupositionalist, moral, etc...), how do we establish this being is the author of the scripture, based on the scripture only? Because it claims so in the book? This kind of claims come by the dozen and are cheap. In fact, this very post was directly inspired by God. See? It was cheap.
Only remain faith based arguments. People who claim to "know in their heart" that their favorite scriptures are from God. But this is no rational argument, just a feeling. A hunch is just a hunch, and anybody can reply "well I have a hunch that your hunch is wrong".
It's even radicallý rational. Or fundamentally rational. Or extreme rational. You can choose.
Now why do I say that? Because it is based on another kind of reason you have in mind. It is not the "Ratio" you have in mind. The "Ratio of Enlightment", that is.
Is based on a ratio that doesn't value things in the same way as the ratio of "enlightment". Things that are seen as irrational from one side can be seen as complely irrational from the other, no matter what arguments you use.
You can always try to make people come to your side. This is done already in some way in our school system. The ratio of modern science is already let loose on children the moment they are born and this systematic pressure continues upon entering the school system where very refined slavedrivers (called teachers or professors) try to mold your brain in the rational hardwiring of scientific ratio. The teachers act as if they want the best for the young ones. Well, they probably really think that they want the best for the pupills but that doesn't take away the fact that the pupils are getting a very uniform training. Marginally things like religion are taught but it is the theory of evolution that reigns suppreme.
In this respect the ratio of enlightenment is as radical, extreme, or fundamental as religious ratio. Many people adhering to scientific ratio ridicule non-scientific ratio and laugh at it. The other ratios don't correspond to the Truth. As if that's important. You may of course think that it is important but why making it the absolute standard? It's the same as fundamentalist Christians or Muslims making it absolute standards. You may of course make absolute standards but why forcing young people to adopt them, as is even done in schools in Afghanistan, where besides the islamic standards scientific standards are taught as well (but merely to give the young ones an opportunity for making money in the modern world which already is "Rationalized").
Fundamental rationalists have the nasty habit that they want other people to conform totheir standards. The cruisades are an extreme case and the discovery of the new world by Columbus and its subsequent colonalization are two colloraries. With the ratio of enlightenment the continuing quest for new things (discoveries) would not be there and the will to make others conform to the enlightenment (or at least beat them in submission by newly invented material means) would not be there. The fundamental Nature of monotheistic religion (that already started withXenophanes) shows itself in the assumption that it is thought to be (by it's practitionists) the only one that is true. The same attitude as defenders of the ratio of enlightenment. There, again, is nothing wrong with that but if the insisting becomes obliging (as is done in the modern school system) then you better shake your head while frowning and sigheing.
So, the ratio of religion can be as rational (or irrational, a term many times used to exoress disliking) as the ratio of "Ratio". It can even be just as extreme, radical or fundamental as the ratio of enlightenment. It can be just as fundamental as the fundamental building blocks of Nature that science talks about. It can be just as radical (i.e. its followers) wrt implementing itself in the young ones, converting the non-believers, and maintaining the status-quo. It can be just as extreme too. But at least there are, in most cases, no people involved who wear masks, as the teachers wear in front of the puplis.
So what does this all mean, basically? It means that all ratios are rational and that they can be irrational only from the perspective of one man's rationality. Religeous rationality can be just as extreme as any other rationality. It's dissapointing to learn that scientific ratio is as extreme as fundamental religions are insofar its continuation into the future and spreading around the globe is concerned. It is reasonable that this must be given a closer look with both eyes wide open and the futere of mankind in mind
I don't accept your definition of fundamentalism. Such movements are about some kind of return to fundamentals, correct ethics & behaviours (eg recovering modesty, rejecting 'foreign' practices), & uncompromising reforms/reformations.
Or your definition of irrational as opposed to reason. Love is irrational, unreasoned. But it is not opposed to reason, reasoning and rationality are just irrelevant to that mode of life, where our animal concerns and genes are the relevant way to engage, not our intellect.
I'd look at the way rightwing and conservative views, are linked to threat perception. People living near border conflicts, or experiencing a pandemic, tend to become more hostile to out-groups, and more intolerant of ambiguity.
Wahabism/Salafism, nicknamed 'Islamic puritanism', rose in popularity as the Islamic world experienced a reversal: the loss of the Mughal Empire to the British, the fall of the Ottoman Empire and carving up of the Middle East that led eventually to the creation of Israel. And in the 1970s when the school experienced it's most explosive growth, the imposition of the Shah in Iran against their democratic choice that led to the Iranian revolution and Iran becoming a religious-led state, the Soviet invasion of Afghanistan that led to the creation of the Taliban and Al Qaida, and the huge rise in oil prices following the oil crisees in '73 and '79 that threw a spotlight on Saudi Arabia and amped up Western shennanigans there, where Mecca is.
Robert Sapolsky draws attention to what we would now call OCD behaviours by Luther, in terms of understanding the role of these behaviours in human history, in creating rituals, and on religious governance, in ways that have powerful impacts on cohesion during times of crisis. So we see the rise of protestantism, with the 30 years war, the rising tensions that led to the Defenstration Of Prague, and the English Civil War. The English and Dutch rose from a low base economically and militarily, to dominate the Catholic empires of the Portugese and Spanish, attributed to the so-called 'Protestant work ethic', but more realistically attributable to stricter governance and more judgemental neighbours.
In the history of Judaism, there is a lot of fundamentalist-type behaviour, and OCD ritual. The carrying of the Ark of the Covenant in the desert. The instructions around entering the holy of holies in the temple. And dietary laws - there is a saying 'It's not that Jews keep the dietary laws, it's dietary laws that keep the Jews'.
Chinese rebel religious movements have many times had a zeal towards ethical reform that might be described as the Confucian culture equivalent of puritanism: Liu Bang & the success of the Confucian Han over the brutal Qin; the Yellow Turban, White Lotus & Boxer Rebellions; and the rise of Chinese communism - linked by historians to providing a kind of nationalism that the whole population could participate in. Government antipathy to the Falun Gong, & the Dalai Lama, have to be understood against this background.
Chaos, bad leadership and corruption, lead to reform movements, which often have a fanatical edge. Nationalism in the Weimar Republic, and India & the USA (see rise of conspiracy theories as reaction to loss of trust in regulation & government). The mafia as it started in Sicily, maybe the most invaded bit of the Mediterranean, began as a mode of belonging (rather than purely as a criminal enterprise) that could outlast waves of different rulers who only saw the people there as means to their ends. I link these types of trend to social contracts and game theory here: Is the tyrannicide perpetrated by William Tell morally legitimate?
So, fundamentalism can be intelligible, maybe even seem sensible as a reform movement with the socio-cultural means available. Is, or can it be, rational though? I say no, because these movements are driven by instinctive concerns, the game-theory violation of the social contract, that makes the current situation intolerable, to the point of widespread commitment to change things or die trying.
If you look at Durkheim's understanding of religion, as about social cohesion from the enactment by the community of shared attitudes to sacred things, then you have to recognise the commitment to habeus corpus in the UK, or free speech in the US, as literally sacred values - challenge the value, challenge the basis of cohesion of the community. Jonathan Haidt with his Moral Foundations theory, talks about different cultures having different moral palettes, sensitivity to different dynamics - ie those with purity/sanctity being far more present on the right, those with heightened threat-perception.
These moral-dynamic settings of a community are about game-theory dynamics, and relevant Bayesian priors not just in history but in a culture's narrative of itself (eg US military policy & budget is still living in the Cold War). We don't reason ourselves into our morality, there's no 'ought' from an 'is'. The flourishing of a community or not, is the only true arbiter for an ethical system.
Let's start with the obvious point. If an omniscient being existed, and wrote such a text, it would be highly rational to take it precisely at its word. Reasoning is dependent on assumptions of fact; rationality demands that different conclusions be reached if different foundational assertions are made.
Every faith has two arcs:
The liturgical arc, which is essential for creating uniform teaching and practice within the community
The mystical arc, is useful for moral and spiritual development and understanding
Fundamentalism is (perhaps) an excessive emphasis on the liturgical arc at the expense of mystical insights, but that doesn't make it irrational. It merely means they make assumptions that non-fundamentalists (not to mention secularists) do not make.
