In his use of the phrase “as the older faith used to say,” I believe that Hitchens is referencing not merely the Catholic Church, but the Catholic Church as it existed prior to the Second Vatican Council. At Vatican II, on November 21, 1964 Pope Paul VI promulgated the Lumen Gentium, as a result of which the traditional dogma of salvation significantly expanded to include Christian denominations other than Catholic, and even extended to non-Christians (e.g., Protestants, Evangelicals, Muslims, Hindus, Buddhists, etc., etc.), all of whom had been previously excluded under the older, pre-Vatican II interpretation of "Extra ecclesiam, nulla salus."
Hitchens cleverly contrasts that older faith with Communism (but avoids naming it), subtly making the ironic point that although it explicitly disavowed religion, many astute observers considered Communism a modern, secular (or, Godless) “faith,” one far younger than Catholic Christianity, or any other faith, for that matter. (Wikipedia, Second Vatican Council)
Hitchens cunningly uses the comparative form of the adjective “older” as misdirection, encouraging the reader to assume that by “older faith,” he intends only a comparison between Catholic Christianity and Communism.
Hitchens linguistic legerdemain is revealed however in the next three words, “used to say.” Those three words brought me up short. A moment later I realized that the author intended to convey two different meanings. The first, so readily apparent I was lulled into a false sense of certainty (older faith = Catholicism / less old faith = Communism). The second, occurring slowly, time-released, remaining covert and only implied (used to say = the meaning of Extra ecclesiam, nulla salus prior to Vatican II).
By using the comparative adjective “older” rather than “old,” Hitchens levels a critique not merely at Communism, but also at that other young faith -- the modern, post-Vatican II, Catholic Church.