15 Once the plastic minds of children have been moulded by godless schools, and the ideas of the inexperienced masses have been formed by a bad daily or periodical press, and when by means of all the other influences which direct public opinion, there has been instilled into the minds of men that most pernicious error that man must not hope for a state of eternal happiness; but that it is here, here below, that he is to be happy in the enjoyment of wealth and honour and pleasure: what wonder that those men whose very nature was made for happiness should with all the energy which impels them to seek that very good, break down whatever delays or impedes their obtaining it. And as these goods are not equally divided amongst men, and as it is the duty of authority in the State to prevent the freedom enjoyed by the individual from going beyond its due limits and invading what belongs to another, it comes to pass that public authority is hated, and the envy of the unfortunate is inflamed against the more fortunate. Thus the struggle of one class of citizen against another bursts forth, the one trying by every means to obtain and to take what they want to have, the other endeavouring to hold and to increase what they possess.
Source: Ad Beatissimi Apostolorum (Vatican.va)