Although the State does not have a legitimate interest in preserving a painful and debilitating life that will imminently come to an end, the State does have a legitimate interest in providing positive protections to ensure that a terminally ill patient’s end-of-life decision is informed, independent, and procedurally safe. More specifically, the State has legitimate interests in (1) protecting the integrity and ethics of the medical profession; (2) protecting vulnerable groups—including the poor, the elderly, and disabled persons—from the risk of subtle coercion and undue influence in end-of-life situations, including pressures associated with the substantial financial burden of end-of-life health care costs; and (3) protecting against voluntary or involuntary euthanasia because if physician aid in dying is a constitution alright, it must be made available to everyone, even when a duly appointed surrogate makes the decision, and even when the patient is unable to self-administer the life-ending medication.
http://goo.gl/LajcWR
The Supreme Court outlined the reasoning in its 58-page opinion as follows: