Hannah Arendt:

What makes it so plausible to assume that hypocrisy is the vice of vices is that integrity can indeed exist under the cover of all other vices except this one. Only crime and the criminal, it is true, confront us with the perplexity of radical evil; but only the hypocrite is really rotten to the core.

E.R. Bulwer-Lytton:

It is difficult to say who do you the most mischief: enemies with the worst intentions or friends with the best.