See, this is where I think, before expanding the scope of the Equality Act or the Gender Recognition Act, we need to go back to basics and consider what this legislation was actually for.
People with protected characteristics have, to a greater or lesser extent, suffered discrimination as a result of their protected characteristics. That is what the Equality Act is supposed to address.
We can acknowledge that trans people have suffered discrimination for their decision to live their lives as far as possible as though they were the opposite sex, whilst also acknowledging the conflict of rights which arises if they are included in single sex spaces, services and sports for the opposite sex. The Equality Act does attempt to address this with its single sex exemptions, although many of us think it doesn't go far enough to protect women.
You can, as I do, totally disagree that a woman is something a male person can identify as, and still agree that someone who believes they identify as a member of the opposite sex should not be discriminated against on the basis of that.
But I have to admit that I struggle to see how this is relevant to people identifying as something other than either their own sex or the opposite sex.
What discrimination have people who identify as non binary faced, for example?
Most people identifying as non binary are young and from a generation where being non binary is considered somewhere on the spectrum from "a bit silly, attracting a few eye rolls" to "totally normal" to "fashionable". Older people who identify as non binary, such as Judith Butler, tend to exist in "progressive" enclaves where this is totally accepted.
Non binary people are not denied access to healthcare, or marriage, or parenthood, on the basis of their non binary identity. They are seen by most of the population as being male or female, like everyone else, but choosing to adopt a certain set of beliefs and/or fashion choices. But androgynous women and effeminate men have always existed. People who are part of particular subcultures, such as goths or punks, are probably more at risk of street harassment than non binary people, but nobody is talking about making that a protected characteristic.
If non binary people feel they are being discriminated against because their passport has to say either male or female, or because they can't change their birth certificate to say they are neither male or female, or because their children's birth certificates will list them as either a father or a mother, they're welcome to make that argument. But they need to be aware that what they are arguing for is a new category which should be recognised in law despite it not actually having any identifiable characteristics. Explaining why it is necessary is going to be a rather tall order. And of course it opens the door to hundreds of other categories being added, which seems unworkable. At least allowing people to be recognised as the opposite sex is limited to one particular identity being recognised in law, because there are only two sexes.
If non binary people feel they are being discriminated against in healthcare or the workplace, let's talk about that. Given how insistent the NHS seems to be on the use of inclusive language, it seems to me that non binary people's identities are already acknowledged and respected. As for the workplace, it's more nuanced. What is the actual issue? Are they being misgendered? Are people rolling their eyes? Are people saying they think it's all a load of rubbish? Because to a certain extent, there's not much you can do about that. Even people with religious beliefs, which are a protected characteristic, aren't wholly shielded from that. Do they believe they are being unfairly dismissed or not recruited in the first place because of their identities? Again, this is a thorny issue. Some employers may well admit privately that any CV with "they/them" pronouns on it goes straight in the bin, because they have previous experience of "they/thems" causing trouble with other colleagues if they believe their identity isn't being sufficiently respected. I don't know what we do about that. It's a problem that some members of the TQ+ community have created through their own behaviour, and even if the employer's actions are wrong, it's probably even harder to prove than it is to prove that they have discriminated against a 32 year old recently married woman because they think she'll probably have a baby soon.
At most, it might be helpful to have a court case or some guidance saying that other gender identities not falling within "gender reassignment" should be treated as protected beliefs. Then they would have the same (limited) protection as people with diverse religious or political beliefs.
But adding a new category for people with other gender identities, or even expanding the "gender reassignment" category to include them, seems to me to be going too far. In my opinion, only people who have historically suffered and/or are at ongoing risk of suffering actual discrimination due to their characteristic need to be protected under the Equality Act. Otherwise, we risk undermining the importance of the other protected characteristics, such as being pregnant, or black, or Jewish, or disabled, by equating them to having they/them pronouns.
There's an AMA thread at the moment by a trans man who has been "living as a man" for over a decade, was treated at the Tavistock clinic, has taken all steps to medically transition except for a phalloplasty, which he wants to have, and lives "stealth". He acknowledges that his sex is female and describes his deep distress at his female sexed body which has only been alleviated somewhat by being able to transition. He's a great example of the kind of person the protected characteristic of "gender reassignment" was designed to protect. I don't think we should be watering that down.