It is said that there is no-one more zealous in a cause than an adult convert. A notable example of this was Joseph McCabe, whose conversion was not to a religion, but from religious faith to secularism. Ordained as a Franciscan priest in 1890, and later recognized by the Catholic Church as an able scholar and teacher, by 1897 McCabe had completely lost his faith and had left the priesthood. He became a very active secularist, delivering thousands of public lectures and publishing over two hundred books on a wide range of religious, historical and scientific topics.

First published in 1896, From Rome to Rationalism describes McCabe's journey from faith to humanism. The content was later expanded into a full memoir, Twelve Years in a Monastery.

Like his humanist peers, Robert Ingersoll and Robert Blatchford, McCabe endured persistent vilification for his anti-religious views. It has been noted that much of McCabe's literary output does consist of material critical of the Catholic Church. However, he claimed that he viewed all religions in the same light, and it appears that his focus on Catholicism was due primarily to his previous deep immersion in it, and also to the status of the church as the largest and most influential Christian denomination.