It is a mental illness, some say it is demons, but whatever someone believes in that they are in the wrong body, they're actually mentally sick to see themselves that way. Gender identity disorder, as it's also known.
What is wrong in this society, and it is spreading rapidly, is that rather than being treated for what must be a horrible existence, they're instead being given special rights to trespass on healthy gender's privacy. Public bathrooms, locker rooms, showers, in public schools, as well as in the secular community of many states, is now permitted them by law.
Yes, my 8 year old God daughter can be finishing her swim class at the YMCA, go to the locker room to get undressed and shower and there's a fully exposed male who claims he's a female on the inside, showering in the open! Because it is an open room shower facility there. And he's legally protected! While little Cathy is shocked to her toes!