I think it is as simple as they believe in gender ideology
I think what HH said, is most likely meaning she thinks it's a legal fiction, but there is a good reason for having the legal fiction.
I can kind of understand that position, as in, I can believe that they really believe it.
But wanting to widely extend the fiction and make it "on demand"... makes me doubt how genuine they can be.
I think obviously they don't really believe that "trans women are women", and this is merely the profession of a creed to show their good standing as a member of the left.
Or maybe some people fear looking intellectually unsophisticated and outdated if they don't go with the latest fashionable thinking.
But it is complicated by the fact that it's a real medical issue and many people (correctly) have sympathy for that. Sure it may be right for some people to transition.
But then I also think it's correct to be skeptical of the modern explosion in cases, and correct to be skeptical of parts of the medical profession or others that think this is some settled issue that we need to just affirm people's identities.
You don't see rhetoric from politicians that I would agree with: we shouldn't ban conversion therapy because, actually, on principle, we should be trying to find ways to cure more children and not "affirm" them. Given our lack of knowledge, that's a perfectly reasonable approach, and obviously the healthiest outcome in theory.