As individuals, we are often defined by our differences, not out similarities. We define the “other” by what we are not. The Chinese guy, the homeless guy, the American, the Russian, the rich guy, the gay guy, the adopted guy, the really tall guy etc.
Many, maybe most of the time, these descriptions are labels which are out of the control of the individual. Not always, but more often than not. The adopted guy had no control over being adopted, as the short guy had no control over being short.
I suppose cognitively it is so much easier to remember than:
that girl who lives in the same city, who eats the same food, who watches the same movies, who supports the same team and who goes to the same school. It makes sense to remember the differences, but at what point does it change from a cognitive schema, to something darker, aimed at isolating the other? Making the other feel excluded, abnormal, worthless, maybe even subhuman.
As an example, there is clearly a difference between, “the Chinese guy” and “the gook” and there are many descriptors in between the two, but where does the innocent, “my *insert here descriptor here* friend” become “grayer”, and then turn into the ‘black”.
Where and how does that happen. What is acceptable and what is not?
Never exclude, judge, or stigmatise another human for a trait, or state, which is totally out of that persons control.