You're actually hitting on issues we struggle with in medicine and psychiatry all the time between the principles of autonomy and beneficence. As physicians, we want to take care of patients. The patient also has his or her own autonomy to make decisions.
The tricky part with mental illness is that sometimes the illness can actually undermine the patient's autonomy. That applies to decisional points and processes that I've alluded to before, that idea of having a sense of a foreshortened future, perhaps literally not being able to see that there is a future. If a patient makes a decision because they're unable to see something because of the illness, then how do we reconcile that with full capacity?
I'll give you another example from my own practice. It was just a few weeks ago, actually. I have a patient I've been following for many years. He's chronically suicidal, on and off, and in between actually has good quality of life at times. The latest thing that brought him close to the suicidal state was ameliorated by getting some public transport for him so that he could be a bit more independent and go around the city and actually interact with people. Sometimes when things seem irremediable to a patient in the state of depression, it's because cognitively they cannot see a future. They cannot anticipate that something positive could change. That's part of our role, then, to make that assessment if the cognitive distortions are impairing their decision.