If a flat broke person living on the street, doing lots of drugs, mentally stressed by their circumstance, starts making wild self-aggrandizing claims completely divorced from reality, it isn't controversial to say that person is 'crazy' or mentally ill. People might nitpick the terminology you use to describe that person or criticize you for needlessly drawing attention to it, but nobody goes to bat for the sanity of a homeless person saying crazy shit about themselves.

But if a very rich person living in mansion, doing lots of drugs, mentally stressed by the enormity of their crimes, starts making wild self-aggrandizing claims completely divorced from reality are they crazy? Suddenly people have an interest in defending their mental sanity. Why? Because rich people are entitled to more respect than the homeless by virtue of their wealth, and therefore we shouldn't put common labels like crazy on them? Or maybe it's because a rich luxurious lifestyle makes people immune to the onset of insanity? Were Caligula and Nero not crazy then? On the contrary, I think being very wealthy puts you at greater risk for becoming crazy; the more elite somebody is the more divorced from the typical human experience they become. Power and wealth corrupts their minds, inflating their egos to such an extent they lose track of reality. These people were all crazy. Maybe they weren't "mentally ill" in any biological sense, but they were crazy.

That's part of it, and it's certainly why so many of them have persistent chips on their shoulder about shit that happened in middle school (looking at you, Scott Aaronson).

The other part is that trying to construct all truth from first principles is a hopeless endeavor for a single person or even a group of people. The rejection of institutional expertise - and the collective knowledge of failure modes that is embedded deep within institutions - leads to a lot of predictable failures.