What you and Chu are missing is that mental illness is defined by behavior that is harmful or disruptive to one's self or others, or, as the Mayo clinic puts it: "...a mental health concern becomes a mental illness when ongoing signs and symptoms cause frequent stress and affect your ability to function." It is a disease with symptoms, causes, treatments, etc. So whatever is 'normal' or 'abnormal' is not really a mental health concern. Of course, non-harmful but abnormal conditions used to be classified as mental illness only due to mores of past times, such as listing homosexuality in the DSM. That is something psychiatry institutions try to guard against nowadays. If what the man-girl from the first post is doing is not hurting himself or others, it isn't a mental health concern, no matter how undignified it is.
As for mental illness vs evil, in practice that is decided in courts by juries. As for determining mental illness, here the
criteria for the DSM is relevant, even in determining personality disorders like what many people call 'sociopathy' and what psychiatry terms Anti-social Personality Disorder. What acts deserve jail vs treatment is a much larger debate, of course, but Anti-social Personality Disorder is a real brain condition which has been demonstrated in experiments, it is not just someone who decided to do something bad. Psychiatry certainly doesn't term anyone who commits an evil act to be mentally ill.
