If the doctor hasn't personally examined the person in question, any attempt at diagnosis is guesswork and has a great risk of damaging that person's reputation.
If the doctor has personally done the examination, he/she is bound by professional confidentiality.
If the one attempting to diagnose is not a doctor in the first place, he/she has no business speculating on other people's mental health, and there's still risk of damaged reputation.
It is bad for the reputation of psychiatry — and thus, people's willingness to go to psychiatrists when they would benefit from doing so — if psychiatrists use allegations of mental illness as a social or political stigma.
If you believed you might have a sexually transmitted disease, would you go to a doctor of a school that was known for speculating on how poxy or syphilitic various public figures were, as a way of saying those figures were bad and untrustworthy people?
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