I don't know who would disagree with this statement though. So long as sex (male/female) is not being confused with or conflated with gender (man/woman). But anyhow, the real issue is not about biological sex: it's about the lived identity of gender.
I think a large part of it has to do with which things are or should be segregated by sex, which things are or should be segregated by gender, and which things don't need to be segregated at all.
And this relevant issue - transgender identity - sits squarely and exclusively within the domains of psychiatric medicine, psychology, and sociology (in other words, I disagree that this is an issue upon which the opinions of biologists carry much weight - especially in comparison with those disciplines that I've just mentioned).
I guess that depends on how much influence you think biology has on gender. Differences in brains, for example are biological issues, even if influenced by environment and experience. As are possibilities of genetic factors. when you start talking about genetics, you are talking about biology.
Psychology and biology are fields that interact quite a lot as some conditions are thought to be a result of brain chemistry.
I don't know how many psychiatry and psychology experts in particular disagree with statements of the variety "trans women are women". But I'm hypothesising that there cannot be many. My hypothesis is based upon DSM-5 and its reclassification of transgender identity.
I understand your point here. But I think we should remember that we are talking about terms that predate and were not created by psychology. (man, woman) In other words, they are not psychological terms and arguably are not the authority on how to define the words. They are in the common lexicon as well.
I'm going to use (OMG) and analogy here: Theory. Theory has a significantly different meaning in the biological lexicon than it does in the common. In the common, a theory is a guess. In the Biological (or scientific, really) it means something overwhelmingly supported by the available evidence. Both definitions are correct, but only when applied in context.
We have not reached a point where the term "woman" has been overwhelmingly redefined to be separate from sex in the common lexicon. Most people still use woman and female as synonyms. That has begun to shift, though it's noticeable mostly in discussions about trans-issues, but not to the point where you can say that the old definition is incorrect.
Currently, there are two valid definitions of woman in the common lexicon. The new definition is not really emanating from the psychological community. It's coming from the transgender rights movement. (I'm not sure where it originated, but it is moving into the common lexicon via the trans rights movement.)
The biggest communication problem in this thread is that both sides are holding on to their definition and refuse to speak in the other side's language.