You say ‘even’, as if they’re any better than other religions. All religions are as equally stupid.
You call it an illness is disrespectful in itself.
Now, don’t get me wrong; I don’t ‘buy into’ the ever growing list of ‘genders’. It seems to me that some people just want to feel special.
But who am I to disagree with it; even if I don’t ‘get it’. It doesn’t harm me. So I respect those who feel that way.
As long as I don’t have to ‘change the fabric of my reality’ and call someone a ‘butterfly’, people can call themselves what they want. It’s fine.
As for it being disrespectful; I hope you are aware that people have been calling lots of things ‘illness’ before we truly understood how things worked. Before ‘illness’ it was ‘demonic possession’ or ‘being a witch’ or such nonsense.
Humans like to label things so they’re easily explainable. Easier to judge.
So what you’re doing is basically the same as the people of old branding someone a witch. Think about that for a moment.