Because people use it as an identity.

Can you expand on this? If someone is gay, walking around holding their husband’s hand, does that do it? What if a man is holding his wife’s hand?

Whatever the people that control your life are doing.

I’m not sure I understand. You said you hate politics, but this was your answer for what politics is. Who are the people? Do you have examples of the things they’re doing? Is it like, needing a driver’s license? Tax rates? Spending tax money on libraries? Making abortion illegal?

Difference and diversity is good, division is bad. Division is you’re either on my side or you’re against me.

Let’s say there’s one faction that says, to use a hot button example, “Gay people should not be allowed to marry” and another that says “Gay people should be allowed to marry.” How is a member of faction 1 supposed to interact with faction 2? They are in fact on opposite sides of an issue. Or to use a more extreme example, “Black people should be allowed to eat indoors” versus “Black people should not be allowed to eat indoors”.

Is the problem there the division itself? Would it be okay for you if everyone agreed, no matter which side, so long as they agree to something?

Any decisions made based on race.

This is a common, colloquial, usage of racism. Sometimes people will focus on the large societal level rather than the individual. Per wikipedia:

Academics commonly define racism not only in terms of individual prejudice, but also in terms of a power structure that protects the interests of the dominant culture and actively discriminates against ethnic minorities.[48][49] From this perspective, while members of ethnic minorities may be prejudiced against members of the dominant culture, they lack the political and economic power to actively oppress them, and they are therefore not practicing “racism”.[2][48][55]

I’m not really equipped to debate this usage, but it may be worth keeping in mind that that’s what some people mean. Thank you for answering.

Of course not, please describe that in intricate detail to me. Please spend at least 15 minutes.

Heuristics are generally a cheaper approach to a problem that isn’t guaranteed to be as accurate. Often this is useful when the expense of a more correct approach costs too much in time or other resources. Stereotypes are a kind of heuristic. They’re not always accurate or kind, but they are faster and cheaper.

Honestly I’m not entirely sure I’m using this concept correctly. But what I was getting at was the experience of “All the previous maga-hats I encountered were hostile, so this one might be, too.” It’s not necessarily accurate, but it’s fast, and sometimes that can save your life. Everyone uses this. Unfortunately, lots of us have bad ones, too.