Full Idea
Butler exalts conscience, but appears ignorant that a man's conscience may tell him to do the vilest things.
Gist of Idea
Butler exalts conscience, but it may be horribly misleading
Source
comment on Joseph Butler (Fifteen Sermons [1726]) by G.E.M. Anscombe - Modern Moral Philosophy p.176
Book Reference
'The Is/Ought Question', ed/tr. Hudson,W.H. [Macmillan 1969], p.176
A Reaction
That would appear to be the end of conscience. To make conscience work, it must have a huge authority to back it, and also a fairly infallible means of knowing what it truly says, and that an impostor hasn't replaced it (e.g. via a bad upbringing).