First, I'd recommend everyone (but especially people like doctors, who are in positions of trust and power) take philosophy and ethics courses so that they're better equipped to understand ethical arguments and make their own ethical decisions, without feeling that they must defer to the judgment of "experts".
Second, on the specific issue of when to end care, I think that living wills (when they exist) should be respected and otherwise the judgment of the family should be respected, though the necessary course of action becomes murkier when, for example, the family is estranged from the patient or can't be reached.