I've held my tongue long enough! I'm going to make enemies of both sides with this post.
So we all know that "transwomen" is a no-no and "trans women" is fine, and this shibboleth exists because of the insistence of MTFs that the space indicates that "trans women" are a specific type of woman, while "transwomen" indicates non-womanness. Someone in a previous thread brought up "seahorse" as a reason that "transwomen" could mean "people resembling, but not identical to women or contained in category 'women.'"
So I have to ask: Are TRAs putting sea cucumbers into their garden salads?
Would they be excited to take their children to see the sea monkeys in the zoo?
Would they take a "koala bear" to a bear sanctuary?
Do they think the "vice president" is a type of president?
Are they horrified at the eating of "hot dogs"?
Do they wonder why the cream never turns into "peanut butter"?
By the same token, women who absolutely insist on putting no space in the word "transwomen" because they feel like it, like "seahorse," connotes a resemblance but not belonging in the category:
Is a sunflower not a flower?
A rattlesnake not a snake?
Peppermint isn't real mint?
Seashores must not be real shores, blacksmiths must not be real smiths, sandstone must not be a real stone.
There is no rule in English, not even one of those fuzzy ones where 2 or 3% of words are exceptions, about whether open compounds (with a space) or closed compounds (without a space) connote a specific type of the noun in the compound, or whether they connote a more metaphorical relationship. We use context to understand this complex, non-rule-bound interaction of words.
Why on earth this is a hill anyone has chosen to die on, from either side, is beyond me. Why perfectly reasonable feminists have either bought so deeply into trans rhetoric that they believe a transparently false "rule" about English, or are reacting so deeply against literally anything trans activists say to the point where they'd insist the sky was orange if the TRA said it was blue, is even more confusing.