Why are we people in American society so quick to categorize people and the judge them based on such categories?

btw is Sociology

The United States of America was one of the first countries to historically become a center for cultural diversity, due to the high amounts of immigration it recorded - specially in New York.

Given that many contrasting traditions and physical characteristics could be found among the numerous ethnicities within the population, the most ancient of americans found themselves socially inclined to find a tag for each one of these sets of individuals. Whether it was skin colour, tendencies, outfit style, religious beliefs, or historical background, the stereotypes started emerging from local gossips, and were passed through generations of social constructs and mass media publicity to this day - an epoch when most of these categorizations are stigmatyzed, but live on through the legacy of the elder generations nonetheless.