As I explain in the chapter by that title in Breaking the Spell, “belief in belief” is a common phenomenon not restricted to religions. Economists realise that a sound currency depends on people believing that the currency is sound, and scientists recognise that the actual objectivity of scientific studies on global warming is politically impotent unless people believe in that objectivity, so economists and scientists (among others) take steps to foster and protect such beliefs that they think are benign. That’s acting on belief in belief.
Sometimes the maintenance of a belief is deemed so important that impressive systems of propaganda are erected and vigorously defended by people who do not in fact share the belief that they think is so important for society to endorse. For instance, imbecile monarchs have been kept on their thrones by widespread conspiracies of oblivion and deception when it has been deemed too socially disruptive to confirm to the populace what everybody suspects: the king is an idiot.
Religion offers an extreme case of this. Today one of the most insistent forces arrayed in opposition to us vocal atheists is the “I’m an atheist but” crowd, who publicly deplore our “hostility”, our “rudeness” (which is actually just candour), while privately admitting that we’re right. They don’t themselves believe in God, but they certainly do believe in belief in God.