So restate -- If a person is obviously in such a mental state as to not be able to make a proper contract -- then the refusal should not so easily be accepted -- efforts should be made to suggest -- strongly -- that the patient should accept what will be needed to live. But is the refusal continues even in the face of that cajoling -- it's a refusal. If the person is greviously impaired -- drugged, unconscious or nearly so, seriously dazed and refuses then yes treatment could be started under the assumption that the refusal is ignorable.
But a advance DNR order? That's a vile document unless the person is clearly in their last few days of life -- and even then why not hydrate?
Agree with you on the first part, but not on the advance DNR. You and I may disagree with someone's decision, but I do think it is their's to make.