I know you didn't say anything about affirmation, but would you think it acceptable if someone said they didn’t believe that, for example, a girl could become a boy? And therefore that boys shouldn’t use the girls’ toilets?
Because if you’re not ok with people saying that that’s their belief, it is about affirmation.
I have seen people come here asking for support "My trans daughter has just come out, does anyone have any words of advice"
Answers ranging from "i felt that way as a kid, but worked through it, just give them time" - fine
To "well do you mean your kid has a penis or vagina, if they have a penis don't let them into the womens toilets this is disgusting our rights are being eroded" - not fine on that topic.
"Lots of kids who feel this way are autistic, have you had concerns about this before" - fine
"Hes not your daughter, he is your son, he will always be your son because chromosones" - not fine.
Answers don't need to be affirming, but they don't need to be blatantly rude, upsetting and with the aim of derailing a thread where someone asks for support so it looks like an FWR thread.
There isn't one other subject where it would be appropriate to talk about what genitals a child has and discuss their toilet habits.