The simplest answer is that we are not generally great critical thinkers. Most of what we believe is not based on us personally getting a good education on a topic and carefully weighing the evidence for and against an idea. That is extremely rare.

Most of what we believe is based on or influenced by other factors including biases, the people who raise us, our teachers, our peers, the authorities we recognize and what we prefer to be true.

We are simply not experts in almost everything and do not understand our limitations.

If you look at the things that people believe it is easy to see that the vast majority of them are not things that they personally investigate and verify.

We believe in things that are not true because it us our fundamental nature to believe without sufficient evidence and education.

Conspiracies are things we believe in without sufficient evidence because we tend to believe in everything else that way.

There are other factors involving psychology and relationships at play regarding belief in conspiracies in particular but as human beings we don't usually have sufficient grounds to believe the vast majority of things we believe.

Numerous books have described this such as The Knowledge Illusion and Subliminal by Leonard Mlodinow.

This is a pretty common misconception. To buy Scientology services as a public you will at some point need a lot of money, at least hundreds of thousands of dollars to millions to donate to Scientology.

However, in reality many people in Scientology are not wealthy. Some people are public and buy courses and services that cost hundreds of dollars or thousands and never do the entire training or auditing available simply because they can't afford it. They may do little things like extension courses and read books on their own and hang around for decades.

The vast majority of people in Scientology are not wealthy. The staff in many cases in Scientology orgs and Sea Org members often are very poor people. Many Sea Org members rely totally on the Sea Org for housing, food, clothing and all the basic necessities of life as they have no other savings or income in many cases.

Several thousand people are Sea Org members and several thousand more are staff members. Often for every rich person in Scientology there are hundreds of poor people who are not even thought about by the rich ones. Many rich people don't even acknowledge that the legions of poor people are there to provide them with the services they purchase but most people in Scientology are poor, by a significant margin.

And to be clear, probably less than one percent of people in Scientology make it a significant amount up the bridge. Many people don't make it even halfway to the clear state and of those that do even less make it to the upper level of OT III for example.

The thing that outsiders don't understand is that the upper levels are not attained by most people. I was in Scientology for twenty five years and the people who made it to clear generally went no further, the people who made it to the upper levels had great wealth and were extremely rare and the vast majority of people had little money and never made it to clear. Some people who are middle class or upper middle class spend their life savings to get to clear but that's often where the affordable road ends for them. Most people simply cannot afford the upper levels even if they empty their bank accounts, donate the college fund, max out the credit cards, work sixty hours a week, and sell their houses. Scientology is just far too expensive. You may need several hundred thousand dollars to do your upper levels and most people don't have any way to get that kind of money.

There are a variety of answers and people are complicated. One person might know they are lying and pulling off a fraud while another does not. And other more complex answers exist as well.

Robert Jay Lifton is probably the top living cult expert and he has described the state of a cult leader (guru) having a part of their mind that knows about and works to hide the lies and crimes of the cult leader and another part of their mind that enthusiastically believes what they say, because they want their desires to be true so strongly that they in a deluded state want to assert their will over reality, but to do this you need some awareness that reality disagrees with your desires, even if you deny it.

Lifton has described the state of solipsistic reality in his Book Losing Reality.

Here are several quotes from Robert Jay Lifton:

“In studying people’s behavior under extremity, I have found that the mind can simultaneously believe and not believe in something, and can move in and out of belief according to perceived pressures.”

From

The Assault on Reality | Dissent MagazineMagazine

Here is my interview with Robert Jay Lifton — Bill Moyers

Solipsistic reality means that the only reality he’s capable of embracing has to do with his own self and the perception by and protection of his own self.

— ROBERT JAY LIFTON

From

The Dangerous Case of Donald Trump: Robert Jay Lifton and Bill Moyers on “A Duty to Warn”

So, very often the guru as Lifton describes has in his model, a part of their mind that is believing in their claims, no matter how extreme or outlandish, and another part more firmly rooted in reality that is demonstrated by their own behavior that they use to hide their lies and crimes. Scientology leader Ronald Hubbard took many steps in creating Scientology policy that are designed to hide the failures and crimes of Scientology, things Hubbard had to be aware of to work to hide. David Miscavige today carries on this tradition and hides the failures and crimes of Scientology in his own way.

Several things have proven to be unsuccessful. They are the first things that people want to do - telling people that they are in a cult or stupid or brainwashed is almost always a failure. Cults by design have defenses against these approaches including indoctrination that encourages cult members be prepared for the criticisms they will face.

The cult usually has several thought stopping cliches that answer all criticism and stop critical thinking regarding criticism and steer the thinking and emotions of the cult member towards criticizing the critic (Scientology, for example, trains members that Scientology is the most ethical group on earth and that critics always have hidden crimes and hidden evil purposes that bias them to lie endlessly about Scientology).

When someone has bought into the idea that they should always attack the attacker and relentlessly pursues this it is useless to criticize the cult or the choice of the cult member to join the group. It will just destroy your relationship with the person. If they are talking to you and you have a positive relationship that is your best resource. You have to try to preserve the relationship and not antagonize the person.

Depending on which cult they are in you may have a hard time getting them to look at any information on critical thinking or psychology or cults.

Scientology for example discourages any study of critical thinking, psychology or any thinking on these topics other than Scientology doctrine.

Often people who are in cults need years or decades of seeing the cult itself contradict its own statements. The book A Theory of Cognitive Dissonance by Leon Festinger describes how this process works in fine detail. Quotes below from A Theory of Cognitive Dissonance followed by the page number.

Dissonance has been shown to be an inevitable consequence of a decision. The magnitude of the postdecision dissonance has been hypothesized to depend upon the following factors:
1. The importance of the decision.
2.The relative attractiveness of the unchosen alternative to the chosen one.
3. The degree of overlap of cognitive elements corresponding to the alternatives.
Once dissonance exists following a decision, the pressure to reduce it will manifest itself in attempts to decrease the relative attractiveness of the unchosen alternative, to establish cognitive overlap, or possibly to revoke the decision psychologically. (Page 47)

1. Following a decision there is active seeking out of information which produces cognition consonant with the action taken.
2. Following a decision there is an increase in the confidence in the decision or an increase in the discrepancy in attractiveness between the alternatives involved in the choice, or both. Each reflects successful reduction of dissonance.
3. The successful reduction of postdecision dissonance is further shown in the difficulty of reversing a decision once it is made and in the implication which changed cognition has for future relevant action.
4. The effects listed above vary directly with the magnitude of dissonance created by the decision. (Page 83)

Festinger described how people without preexisting bias on a subject who need to make a decision on that subject seek information. Regarding that subject they seek information of different kinds from different sources and are impartial in what they seek out and willing to take in information of different kinds without concern for either the source or content. They are open to different ideas from different people.

After making a decision some of the information will become consonant in other words in agreement with the behavior chosen and some will become dissonant in other words in disagreement. This will effectively reorganize the information and eventually create bias.

Festinger went on to say:
The presence or absence of dissonance in some particular content area will have important effects on the degree of information seeking and on the selectivity of such information seeking. (Page 126)
Relative absence of dissonance. If little or no dissonance exists, there would be no motivation ( considering this source of motivation alone ) to seek out new and additional information. (Page 127)
The presence of moderate amounts of dissonance. The existence of appreciable dissonance and the consequent pressure to reduce it will lead to the seeking out of information which will introduce consonances and to the avoidance of information which will increase the already existing dissonance. (Page 128)
The presence of extremely large amounts of dissonance. Under such circumstances a person may actively seek out, and expose himself to, dissonance-increasing information. If he can increase the dissonance to the point where it is greater than the resistance to change of one or another cluster of cognitions, he will then change the cognitive elements involved, thus markedly reducing or perhaps even wholly eliminating the dissonance which now is so great. (Page 129)

Festinger here gives us crucial information. If the internal conflict over an idea or behavior is entirely absent a person has no reason to gain information. There are some things a person doesn't care about. A concept may not have any supporting or opposing content in one's mind. So you just don't care.

If you have moderate dissonance, meaning a bit of discouraging information but not too much you avoid disagreeing evidence and seek agreeing evidence. So you might avoid TV shows that disagree with your political views, as an example, and watch ones likely to agree.

For millions of Americans an extreme polarization and self censorship is observable. With as an example Fox news millions of people either agree and only watch Fox news for national political information or strongly disagree and never watch Fox news for national political information.

One could say many of these people have moderate dissonance and seek to reduce it by finding agreement from Fox while avoiding disagreement from others. Now one might say "Why is the dissonance continuing if he only seeks agreement ?", Well he runs into people who don't follow his beliefs or other evidence. So he can stay in moderate dissonance for decades if he doesn't change his routine or get new information of significant influence relevant to the dissonant cognition.

Here is the goldilocks zone of any subject, you care and are not unbiased and open to any information. But you are seeking more proof you are already right and avoiding proof you are wrong. The conditions are just right to keep you close minded and biased towards your beliefs and behaviors. And to keep finding evidence you are right while avoiding evidence you are wrong.

The Scientology cult is built to get a person here subtly, covertly and keep them there.

Now when dissonance is near the absolute limit possible a person changes dramatically. They can seek dissonant information to examine. Why ? Because the way they have been thinking and doing things isn't comfortable and finding small bits of consonant information doesn't relieve the dissonance.

As a simple way to describe this say you get a job at a company and for a while like the pay, work and work environment. It is highly consonant. You don't look for evidence against your job. Simple, then say you find out your company pollutes extensively and uses slave labor in other countries and other unethical practices. Say that is highly troubling to you and you feel tremendously conflicted. It generates high dissonance. You are very concerned on a deep personal level.
At that point just seeing the company logo or motto won't comfort you. A manager just trying to mildly compliment the company won't work. It will merely frustrate you.

In this situation seeking more evidence against your old behaviors and ideas may actually be sought and feel right. Even though you face admitting having been wrong you can dismiss much or all the dissonance involved by changing your mind. All the dissonant elements can be resorted as consonant and the formerly consonant ones as dissonant. So you can entirely switch sides on an issue. For a job you might quit.

Well for Scientologists this has special meaning. When dissonance escalates to explosive proportions the Scientologist can start seeking neutral or critical information on Scientology. Normally Scientologists never do that.

But eventually hearing the same ideas from Hubbard or getting auditing may not relieve doubts about Scientology. So this is the origin of lurkers - the people who secretly look outside the cult and examine the internet at sites like the Underground Bunker and read books critical of Scientology.

In social psychology the three factors of emotions , behaviors and ideas interact. In theory all three are connected and can influence each other. Hubbard stole all three for his methods and renamed and redefined each. He called emotions affinity, ideas reality and behaviors communication. He recognized that manipulating any one could control the other two. I explored that in ARC and KRC.

Cognitive dissonance theory has the concept that with enough dissonance, which for my example can be seen as equivalent to an emotion, one can affect behavior and subsequently beliefs which are ideas. With no concern for something no behavior regarding it is inspired, with slight concern a little reassurance is sought and accepted and with tremendous unrelenting discomfort, even anxiety , internal conflict and worry a person can be driven to look for disagreeing information to settle the issue. They can become open, even slightly, to accepting the criticism of their formerly held beliefs. In this way emotions that in the past trapped a person can turn and compel them towards freedom. This level is called explosive dissonance.

The lurkers moved outside the goldilocks zone. Some sadly are so overwhelmed and confused they stop and go back into the cult. So the information they run into is important.

Fortunately many keep up looking outside the cult and begin recovery in earnest. I hope this post has offered an explanation that will help people understand why people stay and why they leave. And to help them recover.

Quotes from:

• Scientology And Cognitive Dissonance Theory

I am not an expert on this subject. That being said, I believe the top promoter of the reptilian conspiracy theory is probably David Icke.

His critics have pointed out that a very large percentage of his ideas are virtually identical to various global cabal conspiracy theories that are anti-Semitic and he has just shifted from blaming Jews and calling them an evil inhuman race to calling shape shifters from a different dimension the villains as either a coded way to promote anti-Semitism. In some countries openly anti-Semitic content will be banned or treated as the hateful ideology it is, meaning most people outright reject it.

So, whether his motivation is plagiarism involving the ideas of others or a genuine support of anti-Semitic beliefs, he is just recycling the false claims that have been made about Jews for centuries.

I think white supremacists will promote his ideas as a sort of gateway to their beliefs, with some people who buy into them making the next step and joining the white supremacists or at least being open to the same beliefs.

It may sound odd but I have discovered personally that many (not all) people who are flat earthers are also holocaust deniers and they start out as flat earthers then graduate to holocaust denial and anti-Semitic beliefs.

So, David Icke for whatever reason has promoted a conspiracy theory that is highly conducive to getting believers to take the next step and become anti-Semitic in their general beliefs.