I am referring to rare instances of 'mercy killing.' For example, a family member in the hospital, stricken with a terminal illness, asking a loved one to administer a lethal dose of morphine, or an injured soldier requesting a colleague to end their life before the enemy captures them. And, of course, the occasional unusual sexual fetish taken to an extreme.
Is there a legal defense in these scenarios? Can one claim "I'm not guilty of murder because they 'consented' to having their life ended?'" - or would it always be murder, or at the very least, manslaughter?