The thing is, I have encounted 100s, no 1000s, of chidren in my professional life. I can say that I've encountered 3 who genuinely came across as sex/gender mismatched and it was constant throughout primary school.
Everyone responded to them appropriately.
However, I have met plenty who just demonstrated preferences that were more commonly associated with the opposite sex. It is these children I am most concerned about, aside from the whole protecting female spaces argument.
I am concerned about the quiet, sensitive year 4 boy who'd prefer to do gymnastics with the girls than play football with the boys and who picks daisies and makes daisychains with the girls on the field at lunchtime. He's definitely a boy and would be quite upset at any suggestion otherwise. I'm concerned about someone suggesting to him that his interest in these things identify him as being 'in the wrong body' and that someone would pursue this on his behalf.
I'm concerned about the year 7 girl who has no interest in dresses or make up, plays rugby and hates her developing breasts because it means she's growing up and she worries that the boys who have, thus far, regarded her as an equal team mate will start to see her differently. She looks at the girls talking about which member of The Vamps they fancy and it's not a world she wants to be part of. I'm concerned that someone might suggest to her that she is, in fact, a boy in the wrong body.
Then, as they get older, they encounter new problems. The 'transgirl' still fancies girls, but none of the lesbians want to know because 'she' has a fully functioning penis and is, actually, quite happy with it and the 'transboy' still likes boys but they're not interested because 'he' doesn't have a penis. Only, under the new law, this will be a hate crime. But problem has arisen because 'she' wasn't actually a lesbian transgirl and 'he' wasn't a gay transboy after all; they were just a boy and just a girl coming to terms with growing up and understanding and establishing their own identify. And, actually, he needed to be told that it's ok for boys to not like football and to like gymnastics and picking flowers and she needed to understand that being at odds with your developing body is completely normal and that she doesn't have to give up rugby because she's a young woman now and she doesn't have to start wearing false eyelashes either.
It doesn't mean that any thing is 'wrong' with you. It's just part of growing up. It means that there isn't just one way of being a boy or just one way of being a girl. Only they will never get chance to realise it because they've been taking hormone blockers and their puberty and sexual development is fucked.
All this new law will do is tell us that the gender stereotypes that have developed over the years and that some people have fearfully stuck to are, in fact, natural law. When they are not. You can have a penis and wear eyeliner or cry at Love Actually. And you can have a vagina and drink pints and swear like a trooper. And you can be either a boy or a girl and you can do both (I do).
That is what really worries me about it.