Should our criminal law punish voluntary euthanasia in its active and passive forms?
Where a terminally ill person voluntarily, intelligently, and knowingly chooses to die with someone's help, the person who knowingly assists the death by active conduct should not be liable for murder or assisting suicide, i.e., voluntary euthanasia of the terminally ill should be legal under controlled circumstances.
Where a terminally ill person voluntarily, intelligently, and knowingly chooses to die with someone's help, the person who knowingly assists the death should be liable for the crime of murder, not aiding (assisting) suicide.
Same as the previous answer, except that the person who knowingly assists the death should be liable for the crime of aiding (assisting) suicide rather than for the crime of murder.

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Voluntary euthanasia refers to the act of being put to death painlessly as a result of voluntary request. It is equivalent to assisted suicide. Assisted suicide is legal in the states of Oregon (via the Oregon Death with Dignity Act), Washington on March 5, 2009 (by Washington Initiative 1000), and Montana (through a state supreme court ruling on 12-31-09 in Baxter v. Montana, 224 P.3d 2111 (Mont. 2009)). In these three states, subject to substantial hurdles, people are allowed to kill themselves with drugs prescribed by a doctor for such purpose. For example, under Oregon's voter-approved Death with Dignity Act, a terminally ill patient may obtain the lethal drugs if two doctors agree that the person has less than six months to live and is mentally competent to decide whether to end his life.  See  How to Die in Oregon (2011) an HBO presentation documenting how terminally ill patients in Oregon co hoose assisted suicide. See Gonzales v. Oregon, 546 U.S. 243 (2006); Washington v. Glucksberg, 521 U.S. 702 (1997).

The majority of states, over 40, have laws making it a statutory crime to assist or aid suicide, e.g., TPC Section 22.08 (Aiding Suicide), or rely on the common law crime. (1),(2)

In fact, physicians have been knowingly (aware that their acts are reasonably certain to cause death) hastening the deaths of their patients since antiquity. They do it many times every day in the USA with "P.R.N." orders. P.R.N. means pro re nata (administer as needed or as the situation arises). When coupled with a morphine drip, the result of a P.R.N. order by a doctor is death by overdose of morphine.  There is no accurate frequency data, but this could be accumulated easily by doing drug screens on people who die in hospitals. I suggest to you that perhaps 60% of the geriatric deaths would display lethal doses of drugs, principally morphine, that are given in IV drips to "alleviate pain" under a P.R.N. order. Analytically, these are murders under the common law, Model Penal Code, and law of Texas because they are done knowingly, though not necessarily with intent to kill. See Section 19.02 (b) (1) TPC . I also submit that there is also a significant amount of low visibility (bootleg) euthanasia in connection with full-blown terminally ill AIDS patients in extremis. (1-Final Exit), (2-pdf article), (3)

For further insight, watch online the compelling Frontline Special The Suicide Tourist, the story of a brave man, Craig Ewert, who brings the issue of euthanasia into the light by allowing his struggle with the assisted suicide decision to be documented.
See also Euthanasia, Non-Religious Arguments Against Euthanasia, Voluntary Euthanasia Discussed, Religion and Voluntary Euthanasia, Arguments Against Euthanasia, Pros and Cons of Assisted Suicide, The Case for Assisted Suicide, Essay, Non-Voluntary Euthanasia
  • Kamisar, Yale, Physician-Assisted Suicide: The Problems Presented by the Compelling Heartwrenching Case, Journal of Criminal Law & Criminology, Vol. 88, page 1121 (1998).
  • Kamisar, Yale, Some Non-Religious Views Against Proposed "Mercy-Killing" Legislation, Minnesota Law Review, Vol. 42, page 969 (1958).
  • Newman, Stephen, Euthanasia: Orchestrating "The Last Syllable of...Time", University of Pittsburg Law Review, Vol. 53, page 153 (1991).
  • Williams, Glanville, "Mercy-Killing" Legislation: A Rejoinder, Minnesota Law Review, Vol. 43, page 1 (1958).