No religionist seems capable of comprehending this plain truth. There is this difference between thought and action: for our actions we are responsible to ourselves and to those injuriously affected; for thoughts, there can, in the nature of things, be no responsibility to gods or men, here or hereafter. And yet the Protestant has vied with the Catholic in denouncing freedom of thought; and while I was taught to hate Catholicism with every drop of my blood, it is only justice to say, that in all essential particulars it is precisely the same as every other religion. Luther denounced mental liberty with all the coarse and brutal vigor of his nature; Calvin despised, from the very bottom of his petrified heart, anything that even looked like religious toleration, and solemnly declared that to advocate it was to crucify Christ afresh. All the founders of all the orthodox churches have advocated the same infamous tenet. The truth is, that what is called religion is necessarily inconsistent with free thought.
Robert Green Ingersoll – “Individuality” (1873)