Folklore in medicine has been that the majority of physicians who specialize in psychiatry are at least as mentally ill as their patients, and there is a good deal of evidence to support that.
The US has normalized psychotic thinking. There are people who actually believe that a man can get pregnant and a woman can have a penis, and they aren't considered bizarre or out of the ordinary.
Similar arguments with the WHO:
So why not remove the classification altogether, as was done with homosexuality? Because one of the primary goals of the reclassification is to also improve transgender people’s access to health care. There are often insurance-coverage differences between mental and physical illness, and one of the incentives for the authors of the study would be to close that gap.
https://www.washingtonpost.com/news/morning-mix/wp/2016/07/28/the-w-h-o-says-being-transgender-is-a-mental-illness-but-thats-about-to-change/