Albert Schweitzer, answered from the texts and cited to the page.
The ethic gives no permissions and draws no line below which life may be destroyed without reckoning. The person who destroys life to preserve life remains guilty, and the guilt is not to be legislated away.1234
A person can keep himself clear of it as little as the water can prevent itself from being colored by the dyestuff which is dropped into it. The struggle with thoughtlessness is started and is always going on. But what is the position of the ethics of reverence for life in the conflicts which arise between inward compulsion to self-sacrifice and the necessary upholding of the ego?Reverence for Life, The Ethics of Albert Schweitzer, pp. 79–80
Current ethics has no means of defending the fortress of personal morality because it has not at its disposal any absolute notions of good and evil. Not so the ethics of reverence for life. It possesses, as we can see, what the other lacks. It therefore never surrenders the fortress, even if it is permanently invested.Reverence for Life, The Ethics of Albert Schweitzer, pp. 86–87
A man can keep himself clear of it as little as the water can prevent itself from being coloured by the dye-stuff which is dropped into it. The struggle with thoughtlessness is started, and is always advancing. But what is the relation between ethics and reverence for life in the conflicts which arise between inward compulsion to devotion, and necessary self-assertion?Civilization and Ethics
It has no means of defending the fortress of personal morality, because it has not at its disposal any absolute notions of good and evil. Not so the ethic of reverence for life. That possesses, as we can see, what the other lacks. It therefore never surrenders the fortress, even if the latter is permanently invested.Civilization and Ethics
The constructive centre of the later work, and routinely criticised for lacking exactly the feature it deliberately refuses.