"I do not know what the heart of a rascal may be; I know what is in the heart of an honest man; it is horrible." - Joseph de Maistre
The above quote reminds me of the quote from Samuel Johnson, "I hate mankind, for I think of myself one of the best of them, and I know how bad I am."
I do not agree with the premise of either quote. The authors of such quotes were no doubt too hard on themselves or too cynical about mankind. I believe that most people are good and those who are not are the exceptions or normal people who have been placed in circumstances that have warped their natures.