Out groups not necessary for in group cohesion.

This study offers some insight into the "out-group homogeneity effect (OGHE)."

The OGHE is a cognitive bias found in all humans. Basically, a person tends to view people that are perceived to be different as more similar to each other.

For instance: If you perceive yourself as a member of a minority, then you are more apt to view those not in your minority as being all alike, e.g. "All white people look alike to me or all straight people are homophobes, etc."

The reality is that most people do not fit neatly into such bigoted boxes.