The basis of our convictions (beliefs) are pretty deep, subtle and often well hidden even from ourselves. The are not readily penatrated by hard logic; pounding on them only drives them deeper. Most likely it is the product of something that was valuable long ago in smaller groups where cohesion was highly important for survival. Concerted group effort was more important than hard factual explanations that likely were not available anyways.
Some mechanisms do not scale up well, like when the groups get thousands of times larger and the experiences are not so commonly shared. Maybe we will learn other methods to help us work more efficiently together. I think that will be a slow process. Our group identifiers no longer foster co operation; rather they appear to hamper it.
It is as it is!