Of course, like all things related to politeness, there is no absolute rule - if I change my pronouns every week I shouldn't expect people to keep up. But it should not be surprising that you can be fired for not making a minimal effort to be nice to your colleagues.
GP's brusque language aside, can there be any amount of uncertainty on either of these points? Doesn't it seem a bit arbitrary that these two new norms are opposite to each other?
To cite one example: race is considered heritable, and there have historically been harsh consequences of that lineage. In the US, the one-drop rule ensured that anyone with even a single Black ancestor would be subject to the legal discrimination that status entailed (this is called “hypodescent”). So the idea of someone saying “I identify as Black” is… fraught, to say the least.
Still, if there is no other negative effects, then accepting them as a different gender seems like a simple way to ‘heal’ the condition. Certainly in the absence of a way to fix it in the other direction.
I don’t think a lot of people would be well served by accepting that someone is a cat.
Gender dysphoria is real, social contagion is real, and we shouldn't accept or embrace a self-destructive ideology that radically derails the lives of teenagers and younger.
Adults can behave however they want, but it should be considered child abuse to foster transgenderism and transsexuality in minors.
I don't think it is reasonable for you to hold that your definition of gender is the only correct one.