Great post, rebel8. Absolutely. I would only refine it just a bit and state that the degree to which someone is not accepting of truth, is the degree to which they are committed to a particular belief. The question really becomes why are they committed as such? I certainly have my own theories on that, but it goes off-topic.
Overall that hardwired nature of acceptance of things that are untrue has much to do with survival, even if to modern humans and society as a whole, it does far more harm than good. The broader concepts of dissonance theory have quite a bit to say about this, from an evolutionary perspective, both biologically and socially. For example, an animal in the woods that hears what it believes to be a predator, decides to run for cover. That animal does not reason that the potential predator may be nothing more than than the wind ruffling some branches. It makes a decision and commits itself, (even if it means running into a real predator in its efforts to escape).
Humans inherited this fight or flight mentality from our ancestors, and do not always reason when making commitments. If someone commits themselves to a particular belief, the degree to which they have a vested interest in that commitment, is the degree to which they will not accept reasoned discourse with respect to what is real. Their delusion, be it fear driven or otherwise, becomes very real to them, just as that animal trying to escape from what it perceived to be a dangerous threat. Reason does not always prevail, and evolution to a degree, has almost ensured it will not.
d4g