A very reasonable question, but note that for a lot of transgender people gender matters to them even when nothing very dramatic rides on it. They want to be addressed as Alice rather than Alex, to wear women's clothes, and so forth, without being laughed at (or worse) for it, and even if those don't look to the rest of us like "circumstances where gender/sex matters" I'm pretty sure it's a different story when you're looking at it from the inside.
There are rights that accrue to people of one sex but not of the other (to play in one sports team rather than another; to use one bathroom rather than another; ...) but I'm really pretty sure no one goes through the angst and nuisance and embarrassment of gender transition so that they can use a different bathroom.
They want to be addressed as Alice rather than Alex
There are actual woman who are happily want to be addressed as Alex.
People are quite free to want to be addressed in different ways. On the other hand there also a freedom to address someone in multiple ways.
By default we use pronouns via intuition. If a person seems male to us we use "he" is they seem female we use "she". Doing differently takes mental filtering. That carries a cognitive cost.
...They want to be addressed as Alice rather than Alex, to wear women's clothes, and so fo
There are some long lists of false beliefs that programmers hold. isn't because programmers are especially likely to be more wrong than anyone else, it's just that programming offers a better opportunity than most people get to find out how incomplete their model of the world is.
I'm posting about this here, not just because this information has a decent chance of being both entertaining and useful, but because LWers try to figure things out from relatively simple principles-- who knows what simplifying assumptions might be tripping us up?
The classic (and I think the first) was about names. There have been a few more lists created since then.
Time. And time zones. Crowd-sourced time errors.
Addresses. Possibly more about addresses. I haven't compared the lists.
Gender. This is so short I assume it's seriously incomplete.
Networks. Weirdly, there is no list of falsehoods programmers believe about html (or at least a fast search didn't turn anything up). Don't trust the words in the url.
Distributed computing Build systems.
Poem about character conversion.
I got started on the subject because of this about testing your code, which was posted by Andrew Ducker.