The argument goes that while we have the right to refuse treatment, a mentally ill person can't decide what's best for them so the decision has to be made by someone else. However, if people could specify what should happen if they become mentally compromised beforehand, and say that they don't want to be treated, you know if it's them or their disease talking. So what I would suggest is that when people start seeing a mental health professional, they would sign a wavier specifying what should happen in an emergency (and to make changes to it they would first have to undergo an evaluation).
Should such a policy be implemented and if so what would you put on said wavier.