People are little more than hairless chimps: we chatter and squeal (and sometimes kill) anyone we don't recognize as part of our in-group.
We only have the intellectual capacity to identify a small number of individuals personally as part of that group; beyond that we build more ephemeral identities based on communicated reputation and shared biases to identify 'tribes' of commonality with whom we perceive a commonality of interest, at least in the categories of behavior and belief that we feel are personally important.
Outside of THAT, we simply cannot know everyone individually; we base our expectations on stereotypes. What makes those stereotypes to enduring is that they are indeed based on FACT to a greater or larger degree - there is, for example, no stereotype that Asian men have 3 heads or that Muslims breathe water: unfortunately, the building of these stereotypes is rarely today based on personal experience, but on 'shared wisdom' which is just as likely to come from CNN or Breitbart as it is from someone trustworthy.
Finally, this is coupled with a deeply-felt (but never actually proved?) faith in little-L liberal tenets of western civilization: that if we "just communicate more", if we "just understand each other better" we'll all get along better. SIMULTANEOUSLY we profess that people should be coerced as little as possible, that the ideal (in fact, the very essence of democracy) is freedom of choice for each self-aware individual.
I don't believe our ideals are reconcilable with our fundamental animal natures without large scale dictatorial reprogramming. So there's the question: do we get to be ourselves and make free choices, or shall we embark on a Great Leap Forward where a beneficent overclass tells us all how to live so we can be happy?
Frankly speaking: I think John Calhoun's experiments into mouse dystopias are far more predictive of the ultimate outcome of this experiment than some sort of idealized utopia of unicorns and rainbows where we all love each other.