What motivates idiotarianism is the same impulse that motivates true morality: the quest for self-validation through identification with intrinsically worthwhile goals.

Where idiotarianism goes astray is in its pathological conception of what constitute worthwhile goals. Whereas moral people try to discover and embrace that which is conducive to human flourishing; idiotarianism perceives relative success as evidence of malfeasance, and relative failure as evidence of victimhood. The entire intellectual edifice that idiotarians construct is just a rationalisation of what is, at root, an unsavoury emotional disposition, namely a form of self-righteous resentment, writ large.

Put more succinctly, idiotarianism is a rationalisation of a pathological identification with people whose own bad values are the cause of their misfortune.

By the way, I think the term "idiotarianism" obscures more than it reveals. I prefer my own term, "moral inversion", because it brings out the fact that the cardinal error concerns morality rather than rationality, and it captures the Alice in Wonderland quality of idiotarian argumentation, which is characterised by a rational attempt at defending a moral falsehood, rather than by arbitrary irrationality.