Why are people so concerned with binary gender?

Because there are only 2 genders. No other species on this planet has this difficulty seeing the truth. The problem with these "identifying as" or other nonsense is a huge symptom of mental illness, not more than 2 genders. Political correctness is not science nor is it fact based. Honestly it shouldn't be encouraged or enabled here as a place of giving mental health services. If course that's my opinion, I'm sure it will trigger quite a few people, but you can't argue with their and fact. Just because you want to be a mermaid does not make you a mermaid.

I think that religion has a lot to do with it. But also, I think that people can easily understand binary gender. It's simple. Black and white, male and female. But we all know that they world isn't just black and white. Sometimes we have to remind ourselves that though. It's the same with male and female, there's a lot in between the two, but it's easier to see it as just two identities rather than a fluidity. When someone tries to tell us that something "easy" is actually more complicated, people sometimes can be ignorant and refuse to accept it.

That's a question with a very complicated answer. Part of it is that binary gender has been the assumption for most of recorded human history, even though the actual traits and roles expected of each gender vary widely by time and place, and even though there have always been some people with anatomy that made them difficult to classify. It's only very recently that people have started to separate the idea of gender from the idea of biological sex, and once they did that, they could start to imagine genders other than male, female, half-of-each, or nothing-at-all. Part of why people cling to the idea of binary gender is because that's what they're used to, and if they didn't have those patterns and scripts to follow everything might feel chaotic to them. They might actually fear for their lives if binary gender disappeared. Another reason is that binary gender gives men a lot of advantages and privileges because of male domination. Women might also cling to binary gender (and especially to single-sex spaces) in a patriarchal system because they know that they're likely to be safer when men aren't around and when order is maintained, and that they'll have more freedom and autonomy in single-sex environments.

There are two ways I'm reading this question, and since I'm not sure about the original intent, I'll try to answer both, the way I understand this. 1) Why are people against the concept of binary gender? There are many aspects of a person's identity, gender being one of them. When someone identifies a certain way that is frowned upon or discriminated against, this creates an unsatisfactory and unfair situation for this person. If everyone only accepts two genders, we force people to live in a society that is not accepting of who they are. 2) Why do people only believe in binary gender? Many ideas have been understood as "correct" for a very long time. Binary gender has been the norm for a long time, so it's hard to persuade people that there may be other genders as well. A mix of ignorance and inability or unwillingness to understand or accept prevents new concepts from being accepted. Sometimes people also feel threatened by change.

A lot of people's concern with a gender binary stems from the focus on gender roles. Additionally, from a marketing standpoint, it's easier to gender products. You can market items easier if they fall into a gendered category.

It's a matter of cultural construction. We've been taught to believe certain things and to make everything and everyone fit in certain categories. It's not easy for people to let go of their socially internalized beliefs, so dialogue in very important in order to spread awareness of different realities. There are people who would be willing to listen and broaden their horizons, so it's worth trying!

I believe it's a matter of personal comfort and self-awareness. People are often uncomfortable with the concept of non-binary identities when they feel that the existence of such identities threatens their own self-concept (I.e. they may be cisgender, or transgender, but identifying within the binary- and feel that non-binary identities somehow invalidate the gender they understand themselves to be, based on the worldview they've espoused so far) It's much easier to rationalize one's discomfort by pretending that non-binary identities are less legitimate than it is to expand one's worldview to include them.

Perhaps it's because the idea that people can be gender fluid is foreign to them so they find it hard to accept. However, I find that more and more people are beginning to understand and accept this idea :)

People seem to be more concerned with binary gender because it helps them relate to other people. I feel like if it wasn't such a social norm we would be less concerned about it.

well from my opinion because some people don't feel like they fit in into a certain category , everyone is different .some were even born with extra genitals and so on , its complicated , but we have no right to judge