No Stupid Questions

It's engineered into society by power people. if you are too busy looking down on someone. You won't notice them robbing you blind.

Access to knowledge doesn't imply successful absorption of said knowledge. And a lot of the thing isn't about knowledge, but moral premises - things that are neither true nor false, but that you consider good or bad, and as others said here emotions and self-interest play a huge role on the later.

Disenfranchisement is a hell of a drug. A lot don’t believe in the ideology at first, but are forced into it because they lacked proper role models when they were young.

Incels are the easiest to understand. Some people are just unattractive.

Their evidence isn't your evidence. Your curation of facts are never the same as anyone else's. How you interpret these facts are reinforced by your family or friends. If you don't have either you find community where you can. Rinse. Wash. Repeat.

This is the same for many communities. Where a person finds themselves isn't necessarily malicious. They are protecting what they value and think is what makes them unique. That is what makes them dangerous. It's all they have.

Low on Kohlberg

People don't actually guide themselves by Logic.

In fact they undermine their own logical thinking abilities, especially by seeking only that information which confirms that which they already believe in (because it makes them feel to good to "be right") and avoid or deny that information which disproves that which they believe in (because it makes them feel bad to "be wrong").

Even very intelligent people will reach the dumbest of conclusions because of how their own emotions control the inputs to their thinking, the kind of things they think about and even which conclusions they immediately accept without challenge and which they actively try and disprove.

Also add to this that only a small number of people are familiar with the practices of Analytical Thinking (such as used in Science) so are prone to falling for all manner of fallacies and observer cognitive errors (stuff like how one spots mostly that which happens, not the absence of things that should be happening, how others react to one's own non-verbal cues and shape their responses to one's expectations and other such things affecting what one observes and which led to things like Science have double-blind experiments).

Incels at least is a natural consequence of the difference between society's expectations, the needs of an individual, and generally the lack of support and or direct toxicity towards men who need help and emotional support men require as humans.

That one is a societal problem around isolating people away from affection.

The rest I have no freaking clue how one becomes a Nazi in 2024.

Some people have problems in their life and it is convenient to believe they are do to an outgroup. You mention knowledge against it but these people live their lives and insert their instilled prejudices to explain the flaws, making them have (fake) first hand proof of their beliefs.

You'll find a lot of arguments for believing such things if you look for them. Some of these arguments are simply angry rants (and they appeal to angry people who aren't inclined to think analytically) but others are quite sophisticated. Have I refuted all the sophisticated ones I've come across? No, that would take a lot of effort, and maybe some of them are even technically true. I'm not convinced by them primarily because I have certain assumptions about the world: conspiracy theories are generally not true, most people just want to live a good life, kindness is usually reciprocated, and so forth. Someone who holds the opposite set of assumptions (every organization is corrupt, many people are inherently evil, kindness leads to being exploited, etc.) won't be convinced by your "knowledge against it" without even hearing you out in the same way that I'm not convinced by the arguments for it.