I've started to put down my reasons, and I find I'm getting angrier as it goes on. I'm trying to use very factual, non-emotional, language, but it's a bit difficult.
I'm trying to focus on the fact that it isn't a private, individual, thing, (I haven't used "brave and stunning") it's something that has implications for everyone. So, of course, only a diagnosis of gender dysphoria will do. I have the analogy of getting a basic driving licence in mind. That's an individual decision, but it has a heck of lot of implications to the wider society that it's safe to issue a driving licence. But I have also said that a person seeking a GRA is likely to be in a distressed condition, and needs support.
As for the costs: I actually costed up how much for a basic driving licence. It's around £140. I wonder if that's why that figure was originally chosen for a GRA? Of course, a trans person would have to swear a statutory declaration, but that's probably about the same costs as for driving lessons. And there are many other reasons why people need a statutory declaration - should those reasons also be dispensed with? If someone decides to trans - again, that's not a private decision only - should society bear the financial cost of shuffling around that decision?
And I haven't even got on to the questions about sports/single sex/accommodation. It all reads as though this doesn't already happen. Yes, I'll be citing Swim England and Girl Guides, and any other examples I can think of.
Anyway, I've just vented here, so I don't end up writing that "non-binary" is a fucking nonsense.
My thanks to MNetters for a safe space to rant.