The problem with stereotypes though, is that by stereotyping a group of people, you are stripping those people of their individuality in favor of broad generalizations that reinforce your own position and the underlying message usually is "I am better than those people"
It also leads to people clinging to arguments such as "but not all people..." from their groups while going "all the people..." from other groups of people.
That's why "not all white people are racist", but
"all black people entering a vehicle are stealing".