rule

It's so much more fascinating than just that!

So the most well-known of these structures is the bed nucleus of the striae terminalis. The size and number of a specific type of neuron in that region is highly predictive of the gender of the individual, with very high reliability. Postmortem, you can count these neurons and be very close to sure what the sex of the dead person was.

Not only do trans individuals have the structure of the gender they identify as, but there were several interesting controls done to double-check.

First, they looked both at trans people who had undergone different stages of reassignment and compared them to trans people who had not initiated treatment at all. There was no difference, so HRT, etc, is not the cause of the structural differences.

Then they went to a sample of men who were sufferers of specific types of penile/testicular cancers that required a large number of feminizing hormones during the treatment process. Still no change in the striae terminalis.

And then they went back a couple years later and repeated the same experiment, with the same result.

This was all done close to 20 years ago. We've known this for a long time.

Fun addendum: there are a couple types of penile cancer that, sadly, requires the penis to be excised. In 70% of these cases, the men involved experienced phantom penile sensations (phantom limb syndrome). So what's the rate of phantom penile sensations in MTF post-operation trans people? Almost 0%.

that is a confirmed phenomenon that I just call "stanford papers"

I remember back when people wanted to use 'Civil unions' as the term for gay marriage, and have marriage be reserved for religious unions. Then they realized that they had to ammend 10,000 laws that specifically mentioned marriage. Apparently it was easier to change the definition of marriage then to alter that many laws.

A certain fascist comic artist

What one?

Umm, people can definitely change how others view them. And if person A refuses to accept person B for who they are, that doesn’t define person B. It defines person A as an asshole.

You're thinking in the right direction, but you're not quite there. Yes, gender gets assigned at birth as your biological phenotype (because the overwhelming majority of humans identify as cis gender). Humans become individuals and eventually realize that maybe their assigned gender does not fit them. At this point it becomes their own choice and it overrides any gender assignment given at birth. Depending on the individual, gender changes from something that's assigned to something you assign yourself.

That doesn't change much; just means people should place more value in what a person themself identifies with. Some people being inconsiderate doesn't mean others should be too.

Gender isn’t assigned by the individual. Gender is assigned by parents, doctors, the community, and society broadly. Gender is an inherently social construction.

Social/cultural construction doesn't mean that it has to be a collective construction.

Your gender is not different from something like... being a nerd, or being a fan of star wars. Someone might call you a nerd, but ultimately it's up to you to embrace that label or not.

And anyway, cultural things like gender, being a nerd, etc is absolutely unrelated to biology.

This is such a weird take. You're sort of conflating gender assignment with gender perception, while sort of denying gender identity exists, while sort of asserting that gender perception should be authoritative (here lies the bigotry, IMO)

Firstly, the half-denial of gender identity existing / gender applying to individuals

I understand that some people don't identify with the gender that has been assigned to them[...]
Unless your intended tone was mocking and there are some heavy use of air quotes that you did not write, you already accept that a person has their own perception of their gender.

Gender is an inherently social construction. Some people have misconstrued this to mean that gender is an individual construction. It is not. How you see yourself is only part what makes you, you. You are also defined by how others see you.
But how others see you is not "gender assignment". How the community sees you is not "gender assignment". It is gender perception.

The purpose of gender assignment is equally for recordkeeping and for practical purposes in early childhood. Gender is typically assigned by the doctor attending to childbirth, and it's done in accordance to biological sex characteristics because as another commenter mentioned, the majority of individuals are cisgender so it's a sensible default. There are some differences in how you might use the bathroom depending on your genitalia, and (for better or for worse) many social norms, like modesty, are imposed/reflected through gender as well. I think parents of a child also have the authority to choose how they present their child's gender to the world, but this is not something to be done trivially or without the child's best interests in mind, e.g. for attention. It's important to note that one's understanding of their own gender identity is something that develops over time, and will develop differently for everyone.

Just because you see yourself a certain way, doesn't mean others will see you that way, and, again we are defined not only by how we perceive ourselves, but how others perceive us.
Not really. It is more accurate to say that the importance of the balance of others' vs. our own perception is itself a spectrum that will be different for everyone and can change fluidly over time. The battle between how much to value each is in fact a core component of many trans experiences.

On gender perception:

How you see yourself is only part what makes you, you. You are also defined by how others see you.
Have you ever heard the expression "we are not our thoughts, we are our reaction to our thoughts?" The simplest way to put it is that mere perception is not enough to be a definition. The only authority on someone's gender identity is that person. Gender expression is a cognitive shortcut. Sometimes gendered expressions are intentional, sometimes not. There are also agender people who place little or no value on gendered expression in general. If you're interacting with someone in good faith and you are genuinely unsure how you should refer to them, it takes no time at all to simply ask if they have preferred pronouns. It should go without saying that it's not your business to dispute anyone's gender identity, whether they're strangers or otherwise. You are free to think however you want, the problem is expressing those thoughts in ways that cause harm. Like, just don't be a dick?

Unless it’s reasonable for me to address you in business dealings as “smegma John” it seems we might put more emphasis on how someone identifies and wants to be called than what anyone else wants to impose on them

The social construct part of Gender is that the terms were constructed by society - they represented the stereotypes of how different sexes would express themselves. It's in modern times that these are more explicitly detached due to our better understanding of Gender and sex.

People perceive themselves based on their Gender as much as other people do, and it is not necessarily true that a person's perception of themselves (their gender) lines up with their sex - hence Gender dysphoria.

It is one thing to accidentally misgender someone because gender affirmation isn't always outwardly obvious (particularly for non-binary folks), but refusing to make that consideration at all, even when aware of it, would say more about you than it would them.