It seems your issue is more the fact that rationality and reason, as tools of the mind, are not, "infallible."

With the issue of the existence of other's minds, as point of reference.

That is another can of worms entirely.

The idea of some objective truth, or reality does go to the premise of monotheism, that there is some, "all-knowing absolute," in the words of Pope John Paul 2.

Yet is that a viable concept? Logically a spiritual absolute would be the essence of sentience, from which we rise, not an ideal of wisdom and knowledge, from which we fell. More the light shining through the film, than the images and narrative on it.

Ideals are not absolutes. Truth, beauty, platonic forms, etc, are ideals and if we assume them as absolutes, it tends to engender obsessive/compulsive behaviors.

To the Ancients, monotheism equated with monoculture. One people, one rule, one god.

The formative experience for Judaism has the 40 years isolated in the desert, giving us the Ten Commandments. It has always been and still is, looking at Israel today, tribal in spirit and action.

Rome adopted a monotheistic sect as state religion, that had emerged from a combination of monotheism and ancient fertility rites. The son born/reborn in the spring, of the sky god and earth mother. The Trinity.

The purpose this served was the Empire was rising from the ashes of the Republic and it validated top down rule. The Big Guy is in charge. Divine right of kings. Remember democracy and republicanism originated in pantheistic cultures. The family as godhead. When the West went back to populist forms of governance, it required separation of church and state.

So the idea of some complete, all knowing objective knowledge has a cultural foundation, but is it logical?

Don't our minds constantly sort signal from the noise and if we didn't, would sink back into chaos? Knowledge requires some frame of reference, because it is order and order is definition, thus finite. If you try making it open ended/infinite, then it is simply belief, not actually knowing. We only know what we know.

Without that frame to make it signal, it's just noise.

As for other's minds, I find I have much more effective communication abilities, when I let my mind tune into their mind and not just try to fit others into the various pigeonholes and boxes I think they should fit into.

Too much of our culture is about making people fit into boxes, so they are useful tools, or products. Look for where the light shines through the cracks.

The consciousness is the observer. The thought is the observed.