Full Idea
It is nearer the truth to see morality as setting the limits to practical reasoning, rather than being a species of it. Moral principles tell us precisely that we must go no further along the path of calculation.
Gist of Idea
Morality is not a sort of calculation, it is what sets the limits to when calculation is appropriate
Source
Roger Scruton (Animal Rights and Wrongs [1996], p.52)
Book Reference
Scruton,Roger: 'Animal Rights and Wrongs' [Demos 1996], p.52
A Reaction
Well said. If you are assessing whether an act of vicious brutality is required, you have probably already gone morally astray. It is not hard, though, to think of counterexamples, especially in wartime.