The biggest sin?

I was engrossed in my book when a voice spoke from behind me, "You cannot stop a man who knows he is right and keeps-a-coming? What rubbish."
If you read books, you will know that rush of anger which sweeps through you when someone trashes your favorite author's words. The same thing rushed through my veins but, unfortunately, all I could manage was to bleat, "Why do you say so?"
"Of course, you believe it. You are the sort who would believe a Hitler is a saint if he had a way with words or a ...