It's because what EY meant by the psychological unity of humankind was more along the lines of,
... everyone has a prefrontal cortex, everyone has a cerebellum, everyone has an amygdala, everyone has neurons that run at O(20Hz), everyone plans using abstractions.
We might disagree about the last one, but the first four are pretty much fixed.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: