“Humankind cannot bear very much reality” – T.S. Eliot “Burnt Norton”
As with incomprehensible numbers, so too with incomprehensible people. We can be pretty good at 1:1 relationships, (given that we have no direct access to each other’s thoughts), but the human brain has difficulty keeping track of pluralities. Any more than three other people, all running around in different directions, bizarrely and waywardly doing their own varied and inconsistent things, and we’re flummoxed.
It is far easier if we can treat them like a single entity, all acting in unison, in lockstep, if we can apply a generalised theory, a formula, to everyone in a category: a narrative. A story. We can lock a whole group into one body and then imagine it relating to others as if it was a single person and this makes it so much easier to understand, just as “a million” becomes a word-symbol that can relate in specific grammatical ways to other enormous numbers and leave us with the illusion of understanding.
This is fine if people can be used interchangeably. The predator needs to predict the movement of the herd only well enough to catch any one of its members. The problem begins when we start to generalise about societies numbering in millions, discounting any variation or individuality as anomalous, and then impose our averaged-out conclusions back onto the individual members of that group.
This is a particularly pernicious practice when you are investigating something as evanescent as attitudes and states of mind. Then, if any of your subjects has doubts about what you are attributing to them, you can claim that they are unaware of their own “unconscious bias”. Then your conclusions, no matter how erroneous, cannot be falsified. That makes your argument scientifically invalid, of course, and yet, ironically, makes it appear unassailable.
 Singularising whole ethnic groups used to be a perfectly respectable way of talking about them: “The Pathan is a man of strange, brutal honour”, the Victorians or Edwardians might have said, “The Oriental is a wily chap.”