I used to live near an Orthodox Synagogue. Because of their religious belief, Orthodox Jews do not drive on the Sabbath; they walk to services every Friday night; therefore, they strongly prefer to live in close proximity to their Synagogue.
Since the Synagogue was on a busy street, I walked through often, and came to recognize a distinct style, big bushy beards, a certain kind of flat-brimmed hat, the cut of overcoat, the somber colors.
I’m sure, for natural reasons, that these birds do flock together. But there are no hard-and-fast boundaries. If we were to inspect the demographics, we’d probably find many Orthodox families grouped in distinct clusters. We’d also find some areas where Orthodox and Gentile intermingle to some degree.
There was no “border control.” Nobody barred my passage through the neighborhood. It’s quite probable that if I’d taken a shine to some potential mate therein, the family would have steered us apart. There were no artificial barriers to conversation and commerce, but my actual intercourse with these neighbors was slight.
Bordertarians leap from these natural groupings of people to a desire to draw arbitrary lines and borders and post guards to create and enforce this physical separation. That’s quite a extrapolation. Some go even further, and label the mere proximity of people dissimilar to oneself as “forced integration.”