I'm told this quote is from Thomas Paine:
To argue with a person who has renounced the use of reason is like administering medicine to the dead.I experienced this talking to such a person yesterday in my home town. She proceeded to preach to me as if I never preached the same things. So I asked her how often she gets to talk to a skeptic and she admitted hardly ever. I asked if she might be interested in listening to what one of us has to say. She said she wasn't interested. Then I asked, "If what you believe is wrong would you want to know?" She claimed to know she is right and proceeded to preach what I once preached not caring to learn what I knew.