The fact that JK Rowling is in there decrying the fact that she received criticism for dehumanizing an entire demographic makes this letter laughable. She's the one who is really oppressed by society apparently. She lost her entire massive net worth and was thrown in jail over it!? Oh wait, none of that happened, she was just criticized over it. So this is just yet another product of hysterical, exaggerated hand-wringing over suffering the lightest of consequences for one's actions on the internet. I guess that's why they threw Salman Rushdie in there, as if him being included somehow makes his story the same for everybody in it.
It's worth taking seriously even less when you consider how some of those who penned it were tricked into not knowing what exactly they were signing like trans activist Jenny Finn Boylan:
https://twitter.com/JennyBoylan/status/1280646004136697863I guess she was included to as a shield to excuse those like Rowling and grant it some sort of legitimacy.