The first group of people that came to my mind when I thought of thinking of people as a group rather than as individuals were non-Americans. This is a pretty general group of people, but I think that culture plays a big role in the way people think about and view others. It is (relatively) easy for me to interact with Americans no matter where they’re from in the country, their religious or ethnic backgrounds, or political views because we share and understand the same culture. While interacting with someone who is not American, there tends to be more awkwardness and maybe more misunderstandings due to a difference of culture. But when you start actually interacting with individuals who belong to these groups, you begin to see them as individuals rather as a mysterious group.
If you don’t interact frequently with “outsider” groups, then you will not be able to understand their culture. This can lead to some animosity or perceptions of “weirdness” as people can see cultural differences as being rude or impolite. It also allows for people to see a group rather than a set of individuals because their defining characteristics to you may be their physical appearance or their different culture because you don’t know anything else about them. This may lead to a dehumanizing effect on that group of people if you treat them as a monolith.
The social practice of “othering” can lead to exclusion and misunderstandings between groups of people. This can lead to feelings of resentment in both the majority and minority groups as well as promoting a kind of social segregation between groups. It can also lead to the dismissal of people’s culture because it is not understood. Another effect might be poor decisions being made in relation to a group because they’re not properly understood. On a large scale, this can be seen in the American wars in Vietnam, Iraq, and Afghanistan where common complaints are/were that the local situation wasn’t properly understood before entering these areas, making the initial American goals in these areas very difficult to achieve.