To ordinary people, the odious Ian Brady is as mad as a hatter. Nobody who commits the kind of crimes he is responsible for can be “all there”. Whether he is mentally ill, or legally insane is only relevant as far as deciding whether he should be kept in prison or in a secure hospital.
According to the reports on his mental health hearing, he wanted to be declared sane so he could return to prison where he would not face enforced feeding. He claims to be on hunger strike as he no longer wishes to live. For whatever reason, secure mental hospitals will force someone refusing to eat whereas prisons will not.
In terms of deciding whether he was well enough to be returned to prison, it is probable that the right decision was made. Whilst we should not blindly trust mental health care professionals, when they say he is too ill to be returned to prison, we need a very good reason to disagree.
However if Ian Brady had asked a different question; to be allowed to starve himself to death without being force fed, we would have a very different question to answer.
Normally there are very good reasons to force feed someone who is mentally ill and attempting to starve themselves. Some mental illnesses result in depression so severe that suicide seems like the only way out. But after appropriate treatment, the patient can be quite different.
Is Ian Brady suffering from this sort of mental illness? Apparently he is diagnosed as a paranoid schizophrenic, so the answer without additional information is perhaps. If he is not subject to episodes of clinical depression then there may be grounds for stopping the force feeding.
Now of course there is another question to answer here: Should we allow him to commit suicide before he has owned up to his crimes and detailed where the last undiscovered body of known victims is buried?
If we decide that Ian Brady should not be allowed to starve himself to death, it seems reasonable that we let him know the reason why and how he can work towards changing our minds.