Statesboro, GA, USA
I think Lewis' quotation has to be taken with the understanding of his theology. The possibility of deception (self deception being the worst kind) is prominent in his works. Therefore someone doing terrible things believing they are noble things, doesn't mean that they were always considered noble. It doesn't mean that he never had to battle with conscience, misgivings, and a thousand clues to the contrary. My point is ... the distorted belief that can confuse evil with good, is not a testament to the unreliability of conscience, as much as it is to our ability to stifle, callous, and willfully cripple it.
Here's a Lewis quote from his book "Perelandra" to illustrate what I'm talking about:
"It (Dr. Weston) looked at Ransom in silence and at last began to smile. We have all spoken- Ransom himself had often spoken- of a devilish smile. Now he realised that he had never taken the words seriously. The smile was not bitter, nor raging, nor, in an ordinary sense, sinister; it was not even mocking. It seemed to summon Ransom, with horrible naivete of welcome, into the world of its own pleasures, as if all men were at one in those pleasures, as if they were the most natural thing in the world and no dispute could ever have occurred about them. It did not defy goodness, it ignored it to the point of annihilation. Ransom perceived that he had never before seen anything but half-hearted and uneasy attempts at evil. This creature was whole-hearted. The extremity of its evil had passed beyond all struggle into some state which bore a horrible similarity to innocence. It was beyond vice."
And while, I admit that Weston is not a picture of the supposedly "philanthropic" character you are talking about, he still illustrates that the acceptance of evil as good, with no twinge of conscience, is a late stage of corruption ... the rest period of a longer process that involved anesthetizing of conscience along the way.
Nietzsche expressed the same idea (though oppositely to Lewis, not in censure) in The Joyful Wisdom:
"Who can attain to anything great if he does not feel in himself the force and will to inflict great pain? The ability to suffer is a small matter; in that line, weak women and even slaves often attain masterliness. But not to perish from internal distress and doubt when one inflicts great suffering and hears the cry of it- that is great, that belongs to greatness."
Brad, I just think it's a long hard road to get to that point. God made it hard. In "Crime and Punishment" Raskolnikov was blessed enough to fail in his attempts to go down that path.