It seems unlikely that having spent months taking into account all legalities and all the historic case law, including Goodwin, that the expert judges of the Supreme Court remain entirely wrong on the points of law and that conversely, funnily enough, you are correct.
I'm sometimes accused, probably with justification, that I am too wordy. So for the benefit of all readers, I'm going to attempt to be as concise and precise as our friend
@Bromptonaut in my first paragraph at least.
There are many laws that require a deeming provision. This is an establishment in law of the legal status of the person, that is the status from which their treatment must flow. The SC, if read in the spirit of adjudication permitting exclusion as the treatment, it risks setting that all deeming provisions within the scope of UK statute are therefore invalid, and may be interpreted as such.
To use a different example to the GRA, The Immigration Act 1971 ...''Crew members and transit passengers may be
deemed not to have entered the UK.'' This sets out the legal status of the person and the legal basis of their treatment. When a foreign crew member steps onto British land, his treatment is to align with that status. They can not be treated as an asylum seeker, a migrant person, or an invader. The deeming provision 'puts beyond doubt' the treatment of that person.
Here's a second example, Sexual Offences Act 2003 ... 'A child under 13 is
deemed incapable of consenting, full stop.'
Likewise the Gender Recognition Act 2004 ... from memory ... 'Where a full gender recognition certificate is issued to a person, the person’s gender becomes for all purposes the acquired gender.' Therefore the GRA lays the ground of the required treatment in that status.
This is established legal principle and exactly the reason that lawyers were taken by surprise, because the EHRC and other groups leapt on this to mean that the SC at first seemed to be disapplying the deeming provision of another act made in parliament. Under this framing, the SC are said to be ''legislating from the bench''.
So while you may not care about the rights of trans people and their treatment, or even the rights of marine crew members and their treatment, you will surely care at least as much as I do about the legal status of girls and boys from the deeming provision under the Sexual Offences Act 2003. It follows then, that on that basis that if the SC are free to disapply the deeming provision of the GRA, it remains at their will to disapply the deeming provision of the SOA. By legal argument around legal precedence, you might reason that the SC may have done just that.
While you take the position to believe that my only instinct is to care only about my own rights as a trans woman with a GRC, and therefore makes any other view of mine shaky, it is a contemptible belief, and one entirely without evidence.