Only those who have got no conscience, for how can they be tortured by conscience when they have none?
 Fyodor Dostoyevsky, The Brothers Karamazov (1880). copy citation

Context

“In old days we had all sorts, but now they have taken chiefly to moral punishments—‘the stings of conscience’ and all that nonsense. We got that, too, from you, from the softening of your manners. And who's the better for it? Only those who have got no conscience, for how can they be tortured by conscience when they have none? But decent people who have conscience and a sense of honor suffer for it. Reforms, when the ground has not been prepared for them, especially if they are institutions copied from abroad, do nothing but mischief!” source