I am not on board with his slogan.
I think it stigmatises mental illness. He's not saying it in a positive, caring way, is he?
And tbh the abusive members of the trans movement might suffer from any type of illness, but that's not the problem, is it? The problem is the abuse, and the perverts, and the anger, and the demands.
Being trans isn't a mental illness. Being an angry creepy weirdo is condemnable on its own.