John Obrien has brought together a strong indictment of the Catholic Church. With a little effort we could make a similar indictment against the Protestant church and against Islamic and Jewish religious institutions, and others no doubt.
The term "mackerel-snapping” does not communicate any of this indictment. I think Mike Sola is entirely correct in seeing this expression as a slur directed not at the church but at Catholics as such, often with the intent of putting down people of an inferior social status.
