Indeed, in practice Catholic moralizers don't have much of a leg to stand on. I can see "Father" Casey conceding in all apparent humility that Catholics are indeed sinners, which is why they need atheists to be good all the more, to challenge Christians to live up to their ideals. Some such superficial, passive-aggressive show of humility would be in the offing. At least, Catholics would insist that morality is part of the foundation of their worldview, whereas they'd insinuate that atheists have to make it up as they go along.