>>13278513intersex is a birth defect, males and females can be affected differently by the same condition. there are only 2 sexes and only 2 brain sexes. (on tumblr, kiss-the-cis has posts full of resources and studies about the science of brain sex.)
loosely speaking, your brain is male or female. trans men have male brains in female bodies, trans women have female brains in male bodies: this causes gender dysphoria which can only be alleviated with transitioning, which is considered a medical treatment. we already have examples of "in-between" brains, and they belong to normal-ass cis/trans binary people.
"nonbinary brains" make no sense from a scientific standpoint, not to mention, they would be EXTREMELY rare. more rare than trans people. also, have you noticed that "nb" people are almost always teenage girls who are leftists? where's the right wing grandpas that identify as nb? trans and cis people exist in all cultures and all points on the political spectrum, why are nonbinary people exempt?
"3rd genders" in other cultures already exist in western culture, we just have a different name for them. they ALWAYS boil down to one or more of the following: LGB, trans men/women, social roles, crossdressers and gender non-conforming people, eunuchs, and people with intersex conditions. example: the hijra in india are legally are 3rd gender, but when you look at how they define themselves, we would call them trans women.
gender expression is literally just fashion choices.
fuck off with "pansexual", just call yourself transphobic and a retard if you're unironically pansexual. bisexuality already includes everyone, and from an activist/historical standpoint, always emphasized "all genders". pan is for bisexuals in denial who are too scared to call themselves bi.
tldr no gender is not a spectrum, not scientifically speaking. theres men and women, but you can EXPRESS your gender however you choose. stop mixing up FASHION with GENDER.