"mental illnesses" aren't inborn, they're not biological, they're the result of external issues, i.e. how some people are depressed because they're lonely or something society related (although I guess some are more susceptible due to their genes). Similair to how fetishes work (like transexuality/agp). After all, the brain still changes till you're 25.
It's also funny that you even call it a mental illness, that alone makes you transphobic to a big portion of TRAs. Not like it matters, transexuality/gender dysphoria is probably the only mental illness where the solution is not to help them back to reality - but instead to change reality to fit their delusions, that instead of telling them they are and will always be male, they want to make it illegal to even say or think that.
Either way, if it were just seen that way and TRAs didn't push everyone to start denying science and truth for troons' sake, i'd agree, but that's not the case. From women's sports, to women's jails, to puberty blockers for children, to trying to force people to date them or punish them for not saying "ma'am" and "she" to a male - there are a multitude of reasons to hate them.
If it only stayed at "it's a mental illness, don't feed into it by confirming their delusions" and if they didn't push all this shit on others, I'd agree, but as it stands, troons and their activists aren't just harmful to themselves, but to almost every aspect of society, women, children, the people that don't want to fuck them, scientific institutions, etc etc etc.
Either they stop claiming to be something their not and stop with their authoritarianism, or they can KYS themselves
It's not like with gay rights, where "it doesn't concern you" atleast had some merit. Trying that shtick with troons may have worked 10 years ago, but not anymore.