The more one investigates an idea, the more one should come to understand it seeing its positives and negatives. I have studied the idea of gender and its uses for some time now, and I keep coming back to the same conclusions. The elevation of gender over sex is social prejudice at best, social sexism at worst. I want to see what others think.

Definitions:

Sex: The biological expression of a species intended reproductive role
Sex expectations: The biological medians and average that are objectively associated with a sex. For example, men generally have lower octave voices then women
Gender: The non-biological expectations that one or more people have about how a sex should express themselves in public. For example, "Men are expected to wear top hats, women are not."

I do not think there is a debate as to the reality and usefulness of the terms above. The question is about primacy of importance in regards to law and culture. Rationally, which is more important to consider? A person's sex, or their gender?

1. Objective vs subjective

First, sex identification is an objective classification. Gender identification is a subjective opinion. In matters of law sex can be established clearly and unambiguously in most cases, where gender cannot be established with any certainty in any cases. With sex a person can take the attributes of the individual and determine the outcome. With gender, since everyone can have a different idea of how a particular sex should express themselves in society, there is no objective reference. At that point its in the hands of the individual enforcing the law, which ends in disparate ruling across multiple people and inequitable results.

2. Definition of sexism

prejudice or discrimination based on sex OR
behavior, conditions, or attitudes that foster stereotypes of social roles based on sex
https://www.merriam-webster.com/dictionary/sexism

Looking at gender, gender is a social belief that a sex should express itself a particular way. Gender claims are subjective beliefs, not objective facts. Further, it is an expectation that a person express themselves in a way that is not necessitated by their biology.

Lets imagine we have a society that only has one gendered difference between men and women. "Women should cook in the kitchen. Martha does not cook in the kitchen, therefore she is not a woman," that would be sexist. The proper thing would be to tell Martha, "People's expectations of how you should act based on your biology can be ignored. it does not change the fact that you're still a woman." A social belief of how a woman should express themselves elevated above and counter to the realities of their biological existence is simple social sexism.

On the other hand, if William, a male, decided to cook in the kitchen and someone said, "William isn't a man," this would also be sexist. Once again, this is the elevation of a social expectation above and counter to their biological reality. Even further, if William himself stated, "I cook in the kitchen, therefore I'm not a man", this would ALSO be sexist.

Conclusion:

Because gender is subjective and subject to the whims of an individual or group, and placing gender over sex in matters of importance matches the definition of sexism, I just can't see any good reason to consider gender as anything more than a prejudiced and sexist social pressure. We should seek to minimize gender as anything more than an ignorant and potentially bigoted human opinion about people based on their sex.

But maybe I'm missing something. I'm curious to see what other people think.