But, it is objected, there is ground to fear that, when the body is forcibly subjected to the enemy’s lust, the will may be insidiously induced by pleasure to yield consent to sin. Hence, they say, to ward off such sin one is justified in committing suicide, not so much to thwart the enemy’s sin as one’s own. To this I answer that the soul that is subject to God and His wisdom, rather than a slave to bodily pleasure, will by no means give consent to carnal desire when that is aroused by another’s lust. But if it be true—and the truth is obvious—that self-destruction is an abominable and damnable crime, who is so foolish as to say: ‘Let us sin now, lest we sin later. Let us commit murder now, that we may not later, perhaps, commit adultery.’ If wickedness has such control that sin is chosen instead of purity, is not a future and uncertain adultery preferable to a present and certain murder?
Is it not preferable to perform a bad act which may be expiated by penance rather than do a wrong that will leave no room for repentance? I have said this for the sake of those men or women who think that they should do mortal violence to themselves in order to avoid a sin; not another’s, but their own possible sin of consenting to a pleasure provoked by another’s lust.
God forbid that any Christian who puts his trust in God and firmly relies on His aid should give sinful consent to fleshly desires, however aroused. If that rebellious concupiscence which still clings to our mortal flesh follows, as it were, a law of its own independent of the law of our will, its stirrings in the body of one who gives no consent are surely as free from fault as its stirrings in the body of one who is asleep.
Augustine of Hippo, The City of God, Books I–VII