To ask a question would deserve an understanding of what is considered mental illness. Accepting a mental illness as is far different than redefining the term, which seems to be implied in a response as this. The acceptance surprisingly removes some symptoms that would provide a mental illness diagnosis, yet doesn't negate the existence of a mental illness. The problem now is we are in an era of the world where a vocal minority wants to try and dictate this knowledge by completely construing facts of what defines mental illness. Mental illness however does not mean I need to walk around X person with said illness in disgust or in some judgemental manner that would be categorized under that. However, does not change what is defined in the medical field.
http://www.cnsnews.com/news/article/...der-sex-change
Is a good read to understand possible more. Again though, this is just a simple understanding of what you bring up. Not that people should or shouldn't judge these people harshly etc...