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I am confused why people discount reality. It makes no sense. When I tell people facts they don’t like, they say that it’s just my opinion. This mostly happens in church, though. Some people prefer to believe the Bible over actual reality. It’s ok to believe a religion so long as you don’t discount reality, they say, the problem is, that people who believe in religion tend to shut out reality. Fortunately this isn’t everyone, but it is what seems like a large amount.
Sorry for the delay, but while we're reviewing recent history in the thread: they aren't actually discounting reality as much as, like JoshuaFH said, refusing to believe experts. It's an emotional response, not a logical one, and it's also one in which we are, in a weird way, complicit.
We can go into how crank magnetism and self-reinforcing misconceptions happen as a result of the fear of being socially censured for having been wrong, but those are how people go deeper into the rabbit hole. If we look at how people start discounting reality, a lot of it is down to armchair experts getting things wrong. Actual scientists with the time and the inclination for this kind of outreach are vastly outnumbered by people like, well, wierd: amateurs who are passionate about science but lack the time and training to get fully into the weeds about everything they read to the Nth degree. There's nothing wrong with that, but when you put together a long enough chain of amateurs summarizing and quoting each other, errors and spurious references can creep in unnoticed in the details. Sometimes it's little things like misused buzzwords. Sometimes it's bigger things like people claiming carbon dating proves the Earth is billions of years old (right process, wrong radionuclide). Then, once it gets mangled enough, it gets screamed at people by the loudest, smuggest assholes in any given group, along with the strong implication if not explicit statement that only an idiot could believe otherwise, because people tend to assume that anyone disagreeing with them is as dumb as they have to be to be corrected by the facts they understand.
So when you start with a detailed, nuanced scientific consensus and feed it through endless cycles of summary and tech journalism and retweeting until it ends up in the hands of some obnoxious twerp whose point is that everyone else is an idiot, it's not surprising that people would like to prove them wrong, and enough errors creep in along the way to make that relatively easy. Then, once they've proven the consensus-as-shouted-by-twerp wrong, they want to keep going, because we love doing things to extremes. Not only are they wrong that you can look down a canal to prove the Earth is round, they must be wrong about the Earth being round in the first place, and that means a whole lot of experts are wrong too and our poor budding conspiracy theorist is off to prove themselves smart by the most pugilistic methods they've learned from the aforementioned angry shouting, riding their underdog narrative off into the (apparently diffraction-induced) sunset.
It's like the militia asshats who think they can overthrow the American goverment with their bunker full of guns and Krugerrands. They aren't imagining holding off the whole Army, they're imagining them holding off their buddy Hank who's in the reserve and a whole lot of their buddies holding off Hank-equivalent soldiers, which seems like a feasible proposition to them. Similarly, Flat Earthers and similar aren't thinking they're actually going to disprove the scientific consensus by publishing peer-reviewed papers. They're imagining cowing that twerp on the forums, but in a lab coat and on a debate stage, and that seems pretty doable to them.
They aren't discounting reality. They're contesting the idea that the twerps are right about them being stupid, and unfortunately this is the only alternative they can see. Why else would they be so enamored of zeteticism?
Yes and no, and it is ironically (also) something you have also just fallen into;
They believe they are RIGHT. In fact, they go so far as to "know" they are right. (like you just did.)
This is especially poignant, when the thing they claim to have knowledge of is a thing that is intractable to scrutiny, like a divine agency. This is how "Dinosaur bones exist to test your faith!" and similar statements get lobbed around in true earnestness. (In such cases, you need to still be aware that they are not actually arguing against reality, they are making arguments that are grounded in a reality that exceeds the physical. Religion is based on knowledge of supernatural entities, such as gods, who inhabit a supernatural super-universe. Being beings outside the scope of the methods employed by science, they can blithely discount any evidence you provide them; The physical universe is not the TRUE universe-- at least as far as their set of axioms is concerned.) This is mostly the kind of mechanism involved in religious "true belief", but it also gets embroiled, along with the sunk-cost fallacy, when people end up mixed up with conspiracy theories. (EG, the existence of drug induced hallucinations from chemtrails that you must ignore to find the real truth, et al.)
Suddenly, people trying their hardest to show you the history of how Eratosthenes determined that the earth could be generalized as a spheroid better than as a flat plane after observing shadows in wells, are *REALLY* either poor deluded people who have been duped, or are worse yet-- maliciously minded co-conspirators, out to perpetuate the fiction that the earth is not a flat disc, despite the obvious evidence of one's own vision. (ahem.)
I would advise you to remember your training, and recognize that you are falling victim to a confirmation bias here, Trekkin.
By that, I mean your hypothesis is not sufficient. There are other ways people get into the rabbit hole, such as "Profound epiphanies" (such as very vivid dreams, hallucinations, mental changes from traumatic injury, etc), and lack of sufficiently solid education in the face of charismatic believers seeking to actively recruit them. (Born into a cult setting, and suffering sunk cost fallacy issues.)
This does not mean you are wrong; a good deal of people probably do end up in the rabbit hole the way you suggest-- it just is not sufficient to be the single answer, so you should not treat it as such.
My attestation was more in the vein of "Regardless of how they got there, they exhibit this pathology"-- Namely, that no amount of evidence of the falsity of their claims will reverse their belief. (In the case of the religious true believer, it is because the evidence you are providing is based on a subordinate subset of the metaphysical universe they ascribe to, and thus not compelling or meaningful. In the case of the sunken costs narrative, your evidence is indicative of the trickery and systematic malfeasance that seeks to make them conform. [why else would you be so passionate about shadows in wells?] They have invested too much thought into the workings of the conspiracy to be able to recognize the falsity of the conspiracy. The conspiracy has become "true" and unassailable.)