I suppose this varies a lot from individual to individual. I had morphine a few months ago for a shoulder reduction, and I felt horrible enough that I almost wish I'd just done it without painkillers at all.
The evasion and mental gymnastics does have some point at least - it isn't the doctor deciding to take the life of a patient because of a judgement and well any student of the 20th century knows how /that/ can end.
But there are lots of drugs that have the possible side effect of death, and plenty of patients who decide that the risk-benefit of taking a drug is warranted even though it might kill them.
So therefore, everything has to be described in terms of "pain management" and "comfort" where the cessation of breathing is just a... potential side effect. If that, combined with the patient's standing orders not to intubate or perform any sort of resuscitative action in the event that they stop breathing, leads to death... well...
The euphemism that is frequently used is "palliative sedation" (or "terminal sedation", although that seems to be used mostly by people of the thou-must-maximally-suffer school of thought).