They say the religion of your fathers is good enough. Why should a father object to your inventing a better plow than he had? They say to me, do you know more than all the theologians dead? Being a perfectly modest man I say I think I do. Now we have come to the conclusion that every man has a right to think. Would God give a bird wings and make it a crime to fly? Would he give me brains and make it a crime to think? Any God that would damn one of his children for the expression of his honest thought wouldn't make a decent thief. When I read a book and don't believe it, I ought to say so. I will do so and take the consequences like a man.
Speech on Religious Intolerance as presented at the Pittsburgh Opera House (14 October 1879).