Claiming that trans women "shouldn't count as women" isn't being "gender critical," it's being trans woman-exclusionary.
Kathleen Stock (Sussex) has recently begun an effort to encourage philosophers to publicly argue that trans women are not women. I'm planning to write a bit about this, but it is first worth talking about terminology.
How to distinguish between radical feminists that exclude trans women and those that do not is contested. (As is much of the terminology necessary to discuss these issues: L. Mollica discusses the dog whistles in some of Stock's other terminological choices, like referring to trans women as "transwomen," here.) Some on the trans woman-exclusionary side reject that there is any distinction to be made, because they insist there is no legitimate form of radical feminism that includes trans women: including trans women, they insist, is including "men," and anyone who does that is not actually a radical feminist. This would define Andrea Dworkin out of radical feminism.
The nomenclature Stock suggests:
[L]et’s call the position that [trans women] shouldn’t be counted as women, the Gender Critical position, or GC for short (NB I avoid the term ‘TERF’ as it is a slur).
"Gender critical" is a descriptively inadequate designator for this position, and especially inadequate to distinguish between kinds of radical feminism, since opposing gender structures is a necessary feature—the compositional content of “gender critical radical feminism” is something like “radical feminist radical feminism.”
This is not an accident. Calling trans woman-exclusionary positions "gender critical"—like insisting they be called "radical feminism" simpliciter—is designed to position trans woman-exclusion as a straightforward consequence of one of the central commitments of radical feminism. It is not. (I will say more about this soon.)
What distinguishes the view that trans women "shouldn't be counted as women" is of course not that that it is radical feminist or critical of gender, but that it defines womanhood in a way that excludes trans women. And so the acronym 'TERF,' for "trans-exclusionary radical feminist," was coined (or at least popularized) by Viv Smythe, a cisgender woman, in attempt to find a descriptive, evaluatively neutral designator. In response to trans-exclusionary feminists' claims that the term is meant as an insult, she says:
It was not meant to be insulting. It was meant to be a deliberately technically neutral description of an activist grouping. I notice that since TERF has gone out into the wild, many people seem to use trans-exclusive rather than trans-exclusionary or trans-excluding, and I think that leads to some exploitable ambiguity. It is possible to interpret trans-exclusive as “exclusively talks about trans* issues” (which could quite rightly be considered a slam on the rest of their feminism), while trans-exclusionary is more specific that their exclusion of trans* voices and bodies from being considered women/feminists is the point.
It is perhaps unfortunate to find your view generally referred to by a term coined by its opponents rather than its supporters, even one attemptedly neutral. It is also a predictable consequence of trying to camouflage your view within another and insisting that it be referred to only by terms that euphamize rather than describe.
It's true that 'TERF', like other terms for reviled views and their proponents, is sometimes used in a pejorative way. But if TERFs' rejection of the term was based on a desire to avoid a designation sometimes used pejoratively they would of course not want to be called “radical feminists.”
Radical feminism is personally and politically important to me, and so I will not use terms like "gender critical" that disguise trans woman-exclusion within it. I will sometimes use 'TERF' to refer to actual radical feminists that exclude trans women, but will try to avoid it when talking about views in attempt to keep salient the fact that their proponents are often not radical feminists—the rhetoric or merely the name of radical feminism is often co-opted by people who came to trans exclusion by other routes. TERFs also sometimes object to the "trans exclusionary" label on the grounds that they are "inclusive" of trans men. (Whether this "inclusivity" involves accepting trans mens' identities or "including" them in their definition of womanhood seems to vary.) To center trans women as their primary targets, I will try to use terms like "trans woman-excluding" and "trans woman-exclusionary," the most neutral descriptively adequate terms I know. I will sometimes also use "anti-trans" to refer to positions opposing trans people's transitions.
That is my plan, at least.