> If discussing the gender of the crab is politics, then surely assuming the crab is one gender or another is also politics.

A) sane and professional communities just don’t talk about irrelevances like this at all, which is my point

B) if some fringe political belief rejects some standard bread-and-butter assumption, it’s not really useful to describe running with the default assumption as “political”

“If abolishing private property is politics, then surely locking your door is politics.”

If communities want to go down that road, fine, but then they need to get out of this weird limbo where some views are allowed and some aren't. That means that someone must be just as free to say, "I believe the rust crab should have a normal gender because non-gender-binary is not a thing." without getting banned or cancelled. Right now it's reverted to a very don't-ask-don't-tell-like environment where one can either speak in support of such things or not say anything at all, effectively pretending to agree just as in your military example servicemen had to pretend to be straight.

In my experience many people (unfortunately) generally feel free to disparage non-gender-binary concepts on internet communities

Maybe in other places on the internet, sure, but I was referring mostly to the code-of-conduct-gated development communities that pretend not to discuss politics while allowing specific viewpoints above others.

I can see a difference between light-hearted speculation about an imaginary crab's gender and saying that non-gender-binary people don't exist. Can you think of any reason why one of these might be allowed, while the other might not be?

I guess I can't, because they're both political statements. Politics is either allowed or not. I assume, however, you have some reason in mind, by how you phrased the question.

Interesting - well, honestly, not sure how anything wouldn't be political if discussing a crab is politics.

Not that that's necessarily wrong - I'm definitely sympathetic to the argument that the personal is political. But that argument would justify more technical communities taking political stances, not fewer.

Discussing a crab is not politics, but attributing to it a non-existent gender is intentionally contrary to most people's social beliefs (especially outside of the SV bubble) and is thus political. Calling it a normal boy or girl isn't.

If, however, some community members wish to do that, they open to others the option to speak their minds on the topic, including stating that such an action ought not to be taken because no such gender exists. Contrast this with how most "codes of conduct" are written: they would permit community members to speak in favor of such a decision but not against it, as doing so would be "hateful", "bigoted", or "exclusionary".