20 But, what must be confessed, to human minds certain compensative sins do cause such embarrassment, that they are even thought meet to be praised, and rather to be called right deeds. For who can doubt it to be a great sin, if a father prostitute his own daughters to the fornications of the impious? And yet has there arisen a case in which a just man thought it his duty to do this, when the Sodomites with nefarious onset of lust were rushing upon his guests. For he said, “I have two daughters which have not known man; I will bring them out to you, and do ye to them as is good in your eyes: only unto these men do ye no wrong, for that they have come under covering of my roof.” What shall we say here?
Do we not so abhor the wickedness which the Sodomites were attempting to do to the guests of the just man, that, whatever were done so this were not done, he should deem right to be done? Very much also moves us the person of the doer, which by merit of righteousness was obtaining deliverance from Sodom, to say that, since it is a less evil for women to suffer lewdness than for men, it even pertained to the righteousness of that just man, that to his daughters he chose this rather to be done, than to his guests; not only willing this in his mind, but also offering it in word, and, if they should assent, ready to fulfill it in deed.
But then, if we shall open this way to sins, that we are to commit less sins, in order that others may not commit greater; by a broad boundary, nay rather, with no boundary at all, but with a tearing up and removing of all bounds, in infinite space, will all sins enter in and reign. For, when it shall be defined, that a man is to sin less, that another may not sin more; then, of course, by our committing thefts shall other men's committing of lewdness be guarded against, and incest by lewdness; and if any impiety shall seem even worse than incest, even incest shall be pronounced meet to be done by us, if in such wise it can be wrought that that impiety be not committed by others: and in each several kind of sins, both thefts for thefts, and lewdness for lewdness, and incest for incest, shall be accounted meet to be done: our own sins for other men's, not only less for greater, but even if it come to the very highest and worst, fewer for more; if the stress of affairs so turns, that otherwise other men would not abstain from sin unless by our sinning, somewhat less indeed, but still sinning; so that in every case where an enemy who shall have power of this sort shall say, “Unless you be wicked, I will be more wicked, or unless you do this wickedness, I will do more such,” we must seem to admit wickedness in ourselves, if we wish to refrain (others) from wickedness. To be wise in this sort, what is it but to lose one's wits, or rather, to be downright mad? My own iniquity, not another's, whether perpetrated upon me or upon others, is that from which I must beware of damnation. For “the soul that sins, it shall die.”
Source: To Consentius: Against Lying (New Advent)