What makes people irrational thinkers?

[Deesse23]

Never ascribe to malice that which is adequately explained by incompetence

So one vote for incompetence. You genuinely think Belacqua was just so unable to understand his own position and the text being discussed that he spontaneously called out Polymath for being dishonest? Yet the irony in this statement is dripping all over him.

Afaik he is s self-taught "philosopher", or lets say "fan of philosophy", but as in so many cases, a lack of professional education led to exactly what people usually connect with highly trained professionals: Hybris

I think first of all he has a very high opinion of himself, thinly veiled by a cloak of (fake) humility. This is why you see this condescension so often with him. Is he doing this on purpose or isnt he aware of how thin and transparent this "shell" of his is? Idk, you have to ask him.

Imo this is also the reason why he pulled shit like asking Poly to read Harts book in detail and supporting every of his (poly) responses with proper quotes from it, and then, after Poly does exactly that, Bel refuses to return the courtesy* (at least thats my understanding of what happened in the according back and forth). To me this is profoundly unfair and disrespectful.

Secondly, i think there is quite a bit of cowardice involved. The culmination (imho) was reached recently when he openly (as if that was even necessary, his actual position was clear to anyone else anyway) admitted to thinking that (paraphrasing) "evidence is overrated". Only someone suffering from hybris combined with unwillingness to "walk the walk" would hide behind such a statement, although we are often talking about topics outside of the realm of the hard sciences, yet just as often those hard sciences are more than tangentially touched too. You will also see him trying to shift the burden of proof on people.
I can not take someone (too) serious who seems to think facts of reality can be determined by logic/thinking/arguments only. It reeks of a certain lazyness to me.
The whole "metaphysics" shtick is only his very personal attempt to evade the burden of proof every time he is making claims about reality. Even worse, i even have seen him distance himself from the very same ideas he posted days before, by claiming its not his ideas/philosophy but someone elses´ (Aquinas, etc.). In politics something called "plausible deniability" comes to (my) mind.

Incompetence:
Well, i am not saying he knows nothing at all, but (maybe due to being self taught) he certainly seems to suffer from Dunning-Kruger. I am by far not the smartest person in the room/forum, particularly not regarding Philosophy, Kosmology or (evolutionary) Biology (i am rather self taught in those as well), and even i could spot the glaring holes in Harts arguments. Bel seemingly didnt. What else but dishonesty or ignorance is one to assume?

As somebody working in the field of science i have no problem, at all with "non-scientists", people who are fascinated with philosophy (i myself am interested in my free time in everything else but my profession). What i do have a issue with is (much like in my scientific environment) is people who think they are the smartest person in the room and who have no problem with letting everyone know, all.the.time., and on top of that pretending to be somehow humble still.
In the conversations ensuing about various philosophical topics i could tell you half a dozen posters who are apparently better informed, about the ideas they support and the counter arguments as well, have a more profound understanding, but no need to "let you know" all the time. I prefer any post of any of them to anything Bel has to say.

There is probably more to say, but this as much time i am willing to spend on this here and now.

Your mileage may vary, of course.

*saying

I'm also working on other things, so explicating the whole book isn't possible for me right now.

right after he asked Poly to do exactly this, while he is "working on other things".