Some people seem to be anxious around the existence of trans people, the idea of gender being a social construct, or the idea that they can be convinced to go through the wrong puberty. This gender anxiety is due to people wanting to have a firm gender identity or unconscious sex. This does not mean a feminine/masculine gender role. This means, how the person expects their body to be, what hormones would be dominant in their system, their unconscious sex. Most people have this, although it can be quite difficult to notice. The people may believe that trans people existing might threaten their own unconscious sex. "If a man can decide he's a woman, why shouldn't I decide I'm a man for social benefits?" a woman might ask. The thing is, unconscious sex is NOT a choice. Virtually every woman, if she found out that she had gone through a testosterone-based puberty would feel as if her body does not match what she expects it to be. Vice versa for men going though an estrogen-based puberty. This can lead to disgust, despair, anxiety, depression, or what is commonly referred to as gender dysphoria.

You may see people encouraging gender-role atypical people to transition and have a reaction akin to "The trans community is enforcing gender roles!" Unfortunately, it's human nature to assume that most people experience the world as you do. Some people assume that everyone who is feminine wants to be a woman, which is untrue. This can be seen in places such as r/egg_irl, which understandably, causes this gender anxiety that was talked about. Not only is this harmful to gender-role atypical cisgender people, it is also harmful to gender-role atypical transgender people. Trans women can be butch, and trans men can be effeminate.

Some people can not understand unconscious sex and assume that it's related to gender roles. This again, is due to the false assumption that most people experience the world as you do. Some people may legitimately be equally as comfortable in a male body as a female body. And that's okay!

tl;dr gender identity is an innate phenomenon separate from gender roles and physical sex. wanting to be a gender makes you that gender, even if you're not trans.

* I kind of relayed a lot of these ideas from the subconscious sex and intrinsic inclination chapters of Julia Serano's Whipping Girl. Because my memory is somewhat limited, the ideas expressed in the book may be more clear than how I was able to express them.