25 If this teaching, this consoling hope, were taken away from men, there would be no reason for living. Lusts, dissensions, and disputes would erupt from within us. There would be no reasonable check to restrain them. The olive branch of peace would not shine in our thoughts; the firebrands of war would blaze there. Our lot would be cast with beasts, who do not have the use of reason. Ours would be an even worse lot, for we do have the use of reason and by abusing it (which, unfortunately, often happens) we can sink into a state lower than that of beasts. Like Cain, we would commit a terrible crime and stain the earth with our brother's blood.
Source: Ad Petri Cathedram (Vatican.va)