To “stereotype” originally meant to make a mold of the type in a print shop and, from the mold, make copies of it. Every page printed from the resulting type would be identical.
To stereotype people, though, has adverse side effects. When you assume people are alike because of common characteristics, like height, weight, age, race, gender, color, language, likes, dislikes, religion, political beliefs, or income you do them and yourself a great disservice.
To believe that all black people, all Muslims, all males, all police officers, all atheists, all homeless people think or act in a certain way is just wrong thinking. God made us each unique (1 Corinthians 12:12-26) and He loves us all (John 3:16). To lump us in with all others with whom we have one common characteristic is to dismiss most of who we are.
We may be careful not to talk about people in stereotypical terms, but we likely do sometimes act as if the stereotypes are true. As God’s ambassadors to this world, we need to get to know the whole of every individual we encounter.