We begin, as we do in all due-process cases, by examining our Nation’s history, legal traditions, and practices. In almost every State—indeed, in almost every western democracy—it is a crime to assist a suicide. The States’ assisted-suicide bans are not innovations. Rather, they are longstanding expressions of the States’ commitment to the protection and preservation of all human life. Indeed, opposition to and condemnation of suicide—and, therefore, of assisting suicide—are consistent and enduring themes of our philosophical, legal, and cultural heritages. . . .
The Due Process Clause guarantees more than fair process, and the “liberty” it protects includes more than the absence of physical restraint. The Clause also provides heightened protection against government interference with certain fundamental rights and liberty interests. . . . We have also assumed, and strongly suggested, that the Due Process Clause protects the traditional right to refuse unwanted lifesaving medical treatment.
But we “have always been reluctant to expand the concept of substantive due process because guideposts for responsible decisionmaking in this unchartered area are scarce and open-ended.” By extending constitutional protection to an asserted right or liberty interest, we, to a great extent, place the matter outside the arena of public debate and legislative action. We must therefore “exercise the utmost care whenever we are asked to break new ground in this field,” lest the liberty protected by the Due Process Clause be subtly transformed into the policy preferences of the members of this Court.