A saying that gets offered as justification, or rather as an explanation for the beliefs of those fundamentalist, religious followers who hold atrocious beliefs and commit acts of violence, is the dismissive claim that: they're just crazy. That gets offered by those who lack any religious belief, as well as those who have somewhat a religious belief - generally considered moderates. Though dismissing fundamentalists as crazy does do a good job of distancing them from oneself - appropriately so if one is rational - it is a false dismissal. Fundamentalists are not crazy.
First off, let us look at the word fundamentalist: its base is of course fundamental which is based on fundamentalis - the foundation, or primary principles. So we need to look at primary principles. Abrahamic religions have as their base their respective God who is perfect and wrote their respective books (Old & New Testaments, and Koran, for Judaism, Christianity and Islam), and is real with a set of rules. The fundamentalist's God wills and has His preferences; those who follow Him are to obey. Here we shall see that it is not crazy to act with such a belief base, for it is much worse.
Fundamentalist base: genocide is not only permissible, but is commendable. One of the greatest figures to the three Abahamic faiths is Moses. In the book of Numbers Chapter 31, through instruction from God, Moses killed the Midianites, and after seeing all the captives, then declaimed in verses 17-18 "Now kill all the boys. And kill every woman who has slept with a man, but save for yourselves every girl who has never slept with a man." Explicitly, this is genocide and sexual slavery. When Boko Haram kidnapped a couple hundred schoolgirls, they were lambastated, except by other fundamentalists who shared their beliefs. Moses did far worse, but is heralded as a hero. Let's not forget human sacrifice in this for of the 16,000 captives, there were 32 who were 'tribute for the Lord.'
Fundamentalist base: infanticide and sacrificing one's own is commendable. Another hero to the three Abrahamic faiths, and that term gets used because of Abraham. In Genesis Chapter 22, God told Abraham to take 'your son, your only son, whom you love... Sacrifice him there as a burnt offering...' To which Abraham obeys, but right before he slays Isaac, the child is spared and a ram is provided which is sacrificed instead and that pleases God for the willingness to sacrifice his son was a test of Abraham. God did not stay Jephthah's hand, and he offered up his daughter as a burnt offering in Judges 11. When Andrea Yates and Deanna Laney murdered their kids by drowning and bludgeoning with a stone, and did so because they were protecting them from Satan (Yates) or just because God told her to do so (Laney), neither one of them is looked upon as acting properly. Both women were found guilty of homicide, and insane (or trying to get decreed insane).
Fundamentalist base: cult-like slavish devotion to the point of neglecting ones' loved ones and even oneself is expected from the highest. "If anyone comes to me and does not hate father and mother, wife and children, brothers and sisters - yes, even their own life - such a person cannot be my disciple" Jesus' admonition in Luke 14:26. Jesus for Christians, was the Son of God; even those who do not see Jesus as the Son of God still hold a similar belief to their respective one seen as a proxy (Muhammad, Virgin Mary, etc) to God. Whoever is the spokesman for one's creed, must be obeyed and given all to. When David Koresh and Jim Jones tried to convince their followers to abandon all in favor of them and their groups, they were labeled as leaders of dangerous cults, and appropriately so.
Fundamentalist base: men and women are of different value, and women/girls have fewer rights. This can be seen in the sexual enslavement of the virgins aforementioned with Moses (elsewhere male and female slaves - when both are kept alive are treated differently), in the marrying off of teens and children to old men (Jesus' mother Mary was a teen when wed to Joseph and Aisha was six when wed to Muhammad, though nine when consummated), both the bible and Koran declaim women as unclean, and in 1 Corinthians Chapter 14:34-35 "Women should remain silent in the churches. They are not allowed to speak, but must be in submission as the law says. If they want to inquire about something, they should ask their own husbands at home; for it is disgraceful for a woman to speak in the church." The sentiment is equally displayed in 1 Timothy 2:12 "I do not permit a woman to teach or to assume authority over a man; she must be quiet". Not to be let out of the misogyny, the Koran has in The Cow 2:228 that women have rights that are similar to men, but men are 'a degree above them'; in The Clans 33, women are to be covered. Though men and women have their differences, those differences are not in moral value.
Finally, fundamentalist base: Creation is as it is stated in the [their holy] book. Additionally, God can and does change laws of Nature as He sees fit. From this belief emerge evolution deniers, 6000-year-old Earth believers, prayer and faith healers, belief that sex with a virgin will prevent one from being infected with AIDS. To believe the holy books is to believe that which we know is impossible. In Joshua Chapter 10, God stops the sun and the moon for a day so Joshua could finish his victory over his enemies and in The Moon 54:1, God split the moon in two. Such a miraculous base for celestial events make the handling of poisonous snakes as non-problematic; you just need to believe and you will be healed, like Jesus' restoring the sight to the blind or raising Lazarus.
Each fundamentalist base reflects two things; 1) that Nature and reality are but facades to what is true and God can change anything at anytime for any reason, for He is omnipotent, omnipresent and omniscient, so examination of Nature is really futile. If a stick isn't a stick, but a potential snake and dust is a human in waiting, then what really is the reason for studying anything outside God?-why study medicine when one just needs 'faith'? 2) that God chose one and from that, the selected one can commit any atrocity and consider it good because God told him. Whether murdering in mass, or just one's own child, it can be seen as good when told to be done by God, as He has told people to do beforehand.
To believe at a fundamentalist level is to state that the primitive, tribal men had a better understanding of nature and the universe than current scientists. Following that, the moral base was built on tribalism where collectivism was formalized between 'us and them' and others didn't have same rights as one's ingroup; even within the ingroup, there is a hierarchy to abide by - men were the leaders and women were to be subservient. Why is life like this?-it is because it was written. Who wrote it?-God. Who interpreted it, those who had the power.
There is no way that this can be argued. Argument entails claims and definitions to come to truth that can change one's mind with the advanced idea; fundamentalism entails having 'the truth' and making claims and definitions change to fit. How can we rationally argue with one who believes that the sun stopped in the sky?-that the moon was cleft into two pieces?-that a bush was on fire and spoke? How can one rationally make a claim about anything scientific when their base is the negation that science rests upon: that things are what they are, and a stick is not a snake? Similarly, how can one make an argument regarding morality when beloved heroes of fundamentalists were tribalistic, and willing to slaughter those members of outgroups, even kill children.
There is nothing rational to be said to them for they reject reason. However, selectively using the tools of reason, they apply it to their beliefs to further find ways of solidifying belief. There is a furrow on the moon?-proof Allah split it. There are large human bones in
Latin America?-proof of the
nephilim. Others don't have the same
rights, or are even to be killed?-they have chosen the incorrect path and are
aligned with the evil ones. If you try
and contest those assertions, they will point to their holy books as final
evidence and as it is written in them, how can you contest it further? If you contest their holy book, then you are
of the enemy trying to take away their moral base and personal relationship
with divinity - a great threat.
These people are not crazy. They have a definite value system, as well as a methodology within that value system's hierarchy. Within that, they use the tools of logic only so far as to justify a conclusion already embraced and if logic shows it was wrong, then logic itself is incorrect. True reason is every bit an enemy as reality, and that which challenges their belief is not just challenging an abstract notion of what is right or wrong, but one's personal relationship with what is right and wrong as divinely handed down by a specific entity that cares for them. They blind themselves and lash out to threats. The new world is not as much of a concern as the threat to the old; order is important.
We need to better address the issue: 1) address the threat that those who are willing to use force to achieve their ends; 2) address the base of their beliefs, for it is not just wrong, but it is anti-life and anti-reality. When they reject the reality they live both in the physical and moral worlds, and ultimately state this life that we have now is nothing but an impediment to the life that awaits for us after death - what reason can be used to deal with minds such as those?