A deeply confusing factor of this whole debate is the way desires, facts, formation of laws, implementation of laws, and interpretation of facts have been conflated. People are now taking strong stands without a particularly clear view on where things are now, how they are changing with the GRA and what problems the GRA is meant to solve, let alone what the unlooked-for consequences of GRA reform could be. It's like Universal Credit (and dare I say, Brexit) all fucking over again.
When I talk to my fellow lefty types, I tend to start off trying to understand what they think the GRA is going to do. So for people who think it's about equal rights for trans, we get into the current state of "rights" and what we mean by "equal". (This is where we can quickly separate the informed from the hopelessly clueless - I have had a very young student-y type try arguing for the rights of trans & "non-binary" folks to marry, which is easily shot down with a quick good of current UK marriage and civil partnership laws.)
As far as I can work out, in terms of law trans people are not currently unduly oppressed. For example, there aren't glaring unjustices possible such as being legal to rape trans people, stop them from marrying, bar them from gainful employment, throw them out of restaurants, etc.
Now, just because the current laws don't specifically allow discrimination doesn't mean it doesn't happen. (Many woman in the UK can personally attest to that!)
And it may also be that, although the law is generally protective against discrimination, it may be that gender non-conformity needs a particular shout-out in in some areas - maybe, say, employment law. (I'm not saying it does as I haven't looked into it, but I would be open to hearing cases for that, just as I am for making upskirting a specific criminal offense.)
Another area for tackling discrimination would be looking at implementation of law. Women have known for decades that policing has a big impact on how seriously law is implemented, with sexual violence being a significant area where laws have existed but perps have got away with crimes due to police apathy and/or lack of resources and funding. So I would also be entirely open to arguments about how anti-trans discrimination is policed, just as I am open to arguments about the police clamping down on street harassment.
What I DON'T understand is why it's necessary in law to make transwomen women. As so many people on this thread have already said, if you take away the bio-markers (XX, womb, ovaries, biomechanics of having a broader pelvis, etc) defining "woman" to please trans people, then take away the stereotypes (make up, skirts, passive, bitchy) to please women, what exactly do you have left?