Competent to judge: Adventures in hospital ethics

The guy with newly discovered metastatic cancer who was just told of his diagnosis - when he wanted to up and leave, that wasn't crazy of him. Nor was it necessary to call a psychiatrist to judge whether the patient was competent to leave against medical advice. Is there anything magic about psychiatrists which makes them able to judge competence? Some people like titles, and other people like subspecialties. Psychiatrists on call in the hospital become surrogate ethicists, for a reason I don't understand. Because psychiatrists are on call and ethicists are not? Or because we (doctors and everybody else) tend to confuse the legal with the ethical - and we're familiar with psychiatric judgments of mental illness?

It would be too easy - unfair, really - to say that some doctors who think patients are incompetent, or crazy, are unable to see why anyone might disagree with them. But I'll say it anyway.