Here are a few forensic artists' reconstructions of Neanderthals:
And here are a few forensic artists' reconstructions of Homo erectus:
Now imagine that these Neanderthals and Homo erectus had evolved different brain sizes, with correspondingly differing levels of intelligence and inhibition.
Now imagine that one group had created technology, and a written language, while the more primitive group remained in the Stone Age.
Then imagine that some of the Stone Agers tried to live in the society created by the group which had created technology. But since the Stone Agers hadn't evolved the same way, they generally didn't function as well in that technical/industrial society.
Then imagine that the Stone Agers performed relatively poorly on virtually every test of cognition ever developed, and that they had a higher propensity to commit violent crime.
Then, if you can, suspend your disbelief for a moment and try to imagine something really absurd: that anybody who noticed any differences between the two groups was considered a horrible person for having noticed! So, just about everybody had to carry on pretending that there were no differences.
Can you imagine what a horrible mess that world would be?
All I can say is, thank goodness that in our world -- the real world -- all groups evolved the exact same level of cognitive skills!
(Note that I did not say which group was which -- that's your own racist conclusion.)