"Our brains tend to remember facts that accord with our worldview, and discount statements that contradict it. In one Stanford study, 48 students, half of whom said they favored capital punishment and half of whom said they opposed it, were shown two pieces of evidence. One confirmed the claim that capital punishment deters crime, and the other contradicted it. Both groups were more convinced by the evidence that supported their initial position, a phenomenon known as biased assimilation.
This is one reason that propagandists can be effective simply by creating confusion. Unscrupulous campaign strategists know that if their message is initially memorable, its impression will persist long after it is debunked." Nieman Watchdog
People believe what they want to believe. If you live in a community where the shared belief is that dark skinned foreign people are all part of a threat to your own community, then the idea that the world is more complicated than that is easily rejected in favor of a generalized hostility to the outside world.
The same thing applies to dark skinned foreign people. In their communities it is easy to suggest that light skinned foreign people are a threatening force in the world.
Basically, we are all just tribal animals looking for an excuse to hate the opposition, whomever they might be. pl