Thing is, many people have been so conditioned by cultural "othering" that they do not have any qualms with manifesting physical violence based on thought experiments and regional profiling. The "othering" begins in most people's homes, with the family passing on inherited prejudices based on how thoroughly the parents rebelled from their parents ways, in some households parents have completely disregarded prejudices passed to them by those who raised them, but most of the time I see that these old prejudices are replaced by more modern, politically correct prejudices and "otherings"; these prejudices seem harder to eradicate than archaic ones. In families where the "othering" is traditional and follows generational conflicts and historical prejudices instead of modern ones the conditioning on the children can be easier to escape, as these older prejudices are less relevant when compared to modern children's experiences. Per my observation, the issue with borders can come down to these fundamental formative "otherings" and prejudices which become ingrained into individual's worldviews and starting points of opinion.

I propose the most effective way to remove the desire to "other" people you have never met is to abolish the convention of authority and replace it with socially expected communication and respect, with emphasis on unanimous decision making.