Unfortunately, I have succumbed to the confusion italicised below. How do they differ? How is 'supreme value' not equivalent to 'intrinsic good'?
I might have quoted more than necessary; so please feel free to remove text to abridge this post.
There are at least three different ethical approaches to the value of human life. The first approach, often called vitalism, holds that human life is the supreme value. And because of the supreme importance of human life, we should do everything we can to preserve it and never do anything to shorten it.
Doctors should preserve life at all costs, even if the treatment causes the patient considerable pain, even if the treatment's exorbitantly expensive, even if the treatment will succeed in preserving life for only a very short time. Doctors should never do anything that will shorten life such as withholding or withdrawing life-prolonging treatment. Clearly vitalism is a fairly extreme position to hold, and not surprisingly, very few people hold it.
Most people hold to the second or the third approach. The second approach is often called the sanctity or inviolability of life approach. Grounded in natural law ethics, which has historically been very influential in the West, it holds that life is not the supreme good but is a basic good. It's an intrinsic good, which like health, friendship, and knowledge is an important dimension of human well-being and human flourishing.
And because human life is an intrinsic good, we should never intentionally turn against it, never intentionally attack it. It's always wrong, therefore, intentionally to kill another human being. Every human being has a right to life. And the right to life is essentially a right not to be intentionally killed.
But because human life is not the supreme good, it need not be preserved at all costs. The inviolability of life approach is not, then, vitalistic, though it is unfortunately often confused with vitalism. On the inviolability approach, there is a key ethical difference between intending to hasten death and merely foreseeing the hastening of death.
Three Conceptions of the Value of Life
[1.] Vitalism: Human life is the supreme value and we must never do anything to shorten it.
[2.] Sanctity of Life View: Life is an intrinsic good — a good no matter what form it takes — which it is wrong to intentionally end.