30 Further still, if the matter be duly pondered, we shall clearly see these evils to be the more especially dangerous, because, divorce once being tolerated, there will be no restraint powerful enough to keep it within the bounds marked out or presurmised. Great indeed is the force of example, and even greater still the might of passion. With such incitements it must needs follow that the eagerness for divorce, daily spreading by devious ways, will seize upon the minds of many like a virulent contagious disease, or like a flood of water bursting through every barrier. These are truths that doubtlessly are all clear in themselves, but they will become clearer yet if we call to mind the teachings of experience. So soon as the road to divorce began to be made smooth by law, at once quarrels, jealousies, and judicial separations largely increased; and such shamelessness of life followed that men who had been in favor of these divorces repented of what they had done, and feared that, if they did not carefully seek a remedy by repealing the law, the State itself might come to ruin. The Romans of old are said to have shrunk with horror from the first example of divorce, but ere long all sense of decency was blunted in their soul; the meager restraint of passion died out, and the marriage vow was so often broken that what some writers have affirmed would seem to be true-namely, women used to reckon years not by the change of consuls, but of their husbands. In like manner, at the beginning, Protestants allowed legalized divorces in certain although but few cases, and yet from the affinity of circumstances of like kind, the number of divorces increased to such extent in Germany, America, and elsewhere that all wise thinkers deplored the boundless corruption of morals, and judged the recklessness of the laws to be simply intolerable.
Source: Arcanum Divinae (Vatican.va)