Why could believing in stereotypes be harmful to your social development?

If a person believes in stereotypes, they will think that people from certain groups act a certain way. Therefore, when it comes to interacting with others, they may decide not to talk to people from a certain group or even outwardly express their dislike for people of a certain group. Stereotyping is generally frowned upon in today's world, so a person acting in this manner will generally have few people to socialize with.