I dispute this precept vehemently and completely. I'm an atheist, and lots and lots of atheists exist in the world. To me, sacred is simply a nonsense word for a concept I reject.
Life isn't sacred because the sacred does not exist. Religious/spiritual people are deluded in that respect, in my opinion. No evidence supports the existance of spirits or anything else under the "sacred" umbrella.
My own father died in terrible pain and distress, and while he did not technically die by active medical assistance, he wanted to die and he wanted to die as painlessly and with as much dignity as possible.
Fortunately, while assisted dying is illegal where we live, definitions are slippery. His hospice doctor prescribed high levels of sedatives and opiates that calmed him and kept him free of distress, but that also depressed his respiration and without any question speeded his death. Our nurse practitioner told us as much while being very careful how she worded it. I think she said something like, "You'll probably live longer if you don't take the morphine, but do you want to?"
Fortunately for Dad, that practice isn't actually called assisted death, even though it is. Thank goodness!
The torment that Dad experienced in the final stages of COPD is to horrifying to even try to describe.