I do not understand how Celsus, while admitting the existence of Providence, at least so far as appears from the language of this book, can say that there never existed (at any time) either more or fewer evils, but, as it were, a fixed number; thus annihilating the beautiful doctrine regarding the indefinite nature of evil, and asserting that evil, even in its own nature, is infinite. Now it appears to follow from the position, that there never have been, nor are now, nor ever will be, more or fewer evils in the world; that as, according to the view of those who hold the indestructibility of the world, the equipoise of the elements is maintained by a Providence (which does not permit one to gain the preponderance over the others, in order to prevent the destruction of the world), so a kind of Providence presides, as it were, over evils (the number of which is fixed), to prevent their being either increased or diminished!
In other ways, too, are the arguments of Celsus concerning evil confuted, by those philosophers who have investigated the subjects of good and evil, and who have proved also from history that in former times it was without the city, and with their faces concealed by masks, that loose women hired themselves to those who wanted them; that subsequently, becoming more impudent, they laid aside their masks, though not being permitted by the laws to enter the cities, they (still) remained without them, until, as the dissoluteness of manners daily increased, they dared even to enter the cities.
Such accounts are given by Chrysippus in the introduction to his work on Good and Evil. From this also it may be seen that evils both increase and decrease, viz., that those individuals who were called “Ambiguous” used formerly to present themselves openly to view, suffering and committing all shameful things, while subserving the passions of those who frequented their society; but recently they have been expelled by the authorities. And of countless evils which, owing to the spread of wickedness, have made their appearance in human life, we may say that formerly they did not exist. For the most ancient histories, which bring innumerable other accusations against sinful men, know nothing of the perpetrators of abominable crimes.
Source: Against Celsus (New Advent)