They are categories and if we didn't categorize every day, there would be chaos. But when people start to stereotype groups of people, things go wrong. Whether they are positive or negative, stereotypes can cause an enormous amount of conflict. No one fits a stereotype because we're made up of multiple cultures. Someone can be white or black, but they also may be Midwestern, Republican or Catholic.
Research suggests nonverbal communication is even more important than spoken words.
If someone says they're not being defensive and you perceive they are, you will believe the nonverbal cues over the verbal. If they are smiling or using other readable body language, these are signals that are universal. I think one of the strongest examples comes from societies involved in war or strife. A friend of mine from another part of the world told me he had been trained from childhood to think of people from a different ethnic group in an animalistic way. When that happens, the next logical step is annihilation.