Was thinking about the bigger picture in the UK and certainly with our current government the protest against "self-id" has been successful. I'd have said a few years ago that we were on a path that was leading to self-id, I can't see that now happening.
Do people have the same objections to (for example) toilet usage by someone who has got a valid GRC in the UK?
How could anyone tell whether a person who appears male and wants to enter a female space has a GRC? They aren't going to wear it around their neck. As long as some males have the right to access female spaces, and there is no way to know who they are, women lose the right to challenge any male in a female space.
In addition, if sex in the Equality Act means biological sex (as debated on Monday), then having a GRC would not automatically entitled anyone to access spaces according to legal sex.
The whole GRA is a mess and needs to be re-thought from scratch with a clear understanding of what it's supposed to do. It was originally brought in to allow transsexuals to marry somebody of the same biological sex when same-sex marriage was illegal. That no longer applies.
The other reason often given is to allow the sex marker on documents to be changed to align with identified gender ,and to avoid people who have transitioned having to 'out' themselves when showing ID. However, most documents can now be changed without a GRC. An exception is a birth certificate, but this is rarely used for ID and there is an argument that it should not normally be possible to change this when there is nothing objectively incorrect in the original information. If a birth certificate is needed for ID, it should be possible to get around this by having some type of two-part certificate, one with a sex marker that can only be used for very limited purposes where knowledge of biological sex is needed (such as medical procedures or by the police when somebody is convicted of an offence), and another with no sex marker that can be used for other ID purposes.
A GRC is not needed for somebody to have the protected characteristic of gender reassignment and be protected from discrimination in employment, housing etc.
The reason activists pushed so hard for self-ID IMO (apart from needing something to do to justify their status and funding) were largely ideological (sex should be based on feeling rather than objective criteria) and to create uncertainty (as described, where people no longer feel secure segregating anything by sex or objecting to males in female spaces). In addition, changing the birth certificate means that even if the law technically allows segregation based on sex, authorities are faced with a situation where somebody can produce a birth certificate with a sex marker that apparently shows biological sex and they would be then required to prove it isn't. Prisons are an example, where a GRC seems to determine whether or not somebody gets transferred or assessed on a case-by-case basis even though it is not clear that this is legally required.
In my view they need to go back to the start and ask what purposes the GRC is supposed to serve now, then see if there is a way to provide these functions without causing problems for others.