The case for assisted suicide seems to depend on human sympathy — on the impulse toward mercy, the desire to ease what seems like pointless pain and suffering. Why shouldn’t the terminally ill meet death on their own terms, rather than at the end of prolonged agonies? Why shouldn’t the dying depart this earth with dignity, instead of enduring the inexorable stripping away of their physical and mental faculties?

Such are the sentiments that made Jack Kevorkian, who died last week of natural causes, a hero to many millions of Americans. Though he was tried repeatedly and finally convicted of second-degree murder, the former pathologist’s career as “Dr. Death” (he said he assisted at more than 130 suicides) was widely regarded as a form of humanitarianism rather than a criminal enterprise.

But if such sentiments are understandable, they are morally perilous as well. We do not generally praise doctors who help dispatch their terminally ill patients, as Kevorkian repeatedly and unashamedly did. Even when death is inevitable and inevitably painful, it is not considered merciful to prescribe an overdose to a cancer victim against her will, or to gently smother a sleeping Alzheimer’s patient.

The difference, of course, is that Kevorkian’s clients asked for it. That free choice is what separates assisted suicide from murder, his defenders would insist.