Ok my thoughts on calling transwomen men for what it's worth, Obviously these are just my personal thoughts - not everyone will agree and that's cool.
This is complicated so apologies in advance if this goes a bit rambly.
My way of thinking about it is that humans like all mammals are sexually domorphic. That's biology 101 right? Sure there are a tiny percentage of people that are intersex, but bringing that up is just appropriation and is disingenuous. Most (all?) transwomen are male. Penis, sperm, prostate etc.
Now that 'should' be undisputable. Some TA's do and frankly I put them in the same camp as flat earthers.
Where it gets a bit trickier for me is how we define 'man' and 'woman'. The dictionary is usually a pretty good place to start. According to The Oxford English Dictionary:
man
noun
Adult human male.
So according to the dictionary definition I'm a man. In fact all transwomen are men. I've heard people say that it's a morally neutral statement. It's not a judgement statement or meant to be derisory. It's just a statement of fact.
So why do we get so upset at being called men?
I think it's because man means so much more than just adult human male. It has so much social connotation.
connotation
noun
An idea or feeling which a word invokes for a person in addition to its literal or primary meaning.
'Man' invokes all of the thoughts and feelings we have about men in the social context of our society. I can't say that this is the same for all transwomen (and certainly not for transactivists), but to me man means sexist, misogynyst, thoughtless, violent. I have very negative connotations with the word man. I guess to me I just associate the word man with tocxic masculinity.
I once heard a transwoman say "I don't know what I am but whatever it is I'm definitely not a man". Nobody said anything at the time but I know now that pretty much everbody's silent reaction was to think "Who are you kidding? You are clearly a man."
And they are a man. An adult human male. But they desperately didn't want to be lumped under that word which means so much more than adult human male.
I think I've worked beyond this now and I no longer get upset by being called a man or 'he' but I understand why others do. I also don't lay any claim to womanhood or to be called she or her. Some people do call me those things and that's cool. Some people don't and that's also cool.
There is another dynamic that we need to be honest about though. The transgender umbrella has been getting bigger and bigger and men (and I use that word intentionally) who are some of the most vile misogynists I've had the misfortune to encounter claim womanhood, and 'she' and 'her' and have devleloped this culture of entitlement (male entitlement?) and victimhood.
These TRA's harm transexuals so much with their bullshit.
I know that this is a bit #notallmen but I thought it worth trying to explain something from the pint of view of someone who is trans.
Sorry again that was a ramble.