A friend bought this for me after I confessed to my shocking lack of familiarity with Vonnegut's writing. This is described as a memoir but really it's slighter than that - more like a fireside chat with an old guy, albeit a particularly witty and wise old guy with a passion for life that has been undimmed by his years. I will definitely be reading some of his novels after this.
Such suppression of religion was supposedly justified by Karl Marx's statement that "religion is the opium of the people." Marx said that back in 1844, when opium and opium derivatives were the only effective painkillers anyone could take. Marx had taken them. He was grateful for the temporary relief they had given him. He was simply noticing, and surely not condemning, the fact that religion could also be comforting to those in economic or social distress, It was a casual truism, not a dictum.