13 In which proposition these points may well deserve to be questioned: whether such consent is to be accounted as a deed: or whether that is to be called consent which has not approbation: or whether it be approbation, when it is said, “It is expedient to suffer this rather than do that;” and whether the person spoken of did right to burn incense rather than suffer violation of his body; and whether it would be right rather to tell a lie, if that was the alternative proposed, than to burn incense?
But if such consent is to be accounted as a deed, then are they murderers who have chosen rather to be put to death than bear false witness, yea, what is worse, they are murderers of themselves. For why, at this rate, should it not be said that they have slain themselves, because they chose that this should be done to them that they might not do what they were urged to do? Or, if it be accounted a worse thing to slay another than himself, what if these terms were offered to a Martyr, that, upon his refusing to bear false witness of Christ and to sacrifice to demons, then, before his eyes, not some other man, but his own father should be put to death; his father entreating him that he would not by his persevering permit that to be done?
Is it not manifest, that, upon his remaining steadfast in his purpose of most faithful testimony, they alone would be the murderers who should slay his father, and not he a parricide into the bargain? As therefore, in this case, the man would be no party to this so heinous deed, for choosing, rather than violate his faith by false testimony, that his own father should be put to death by others, (yea, though that father were a sacrilegious person whose soul would be snatched away to punishment;) so the like consent, in the former case, would not make him a party to that so foul disgrace, if he refused to do evil himself, let others do what they might in consequence of his not doing it.
For what do such persecutors say, but, “Do evil that we may not?” If the case were so, that our doing evil would make them not to have done it, even then it would not be our duty by doing wickedness ourselves to vote them harmless; but as in fact they are already doing it when they say nothing of the kind, why are they to have us to keep them company in wickedness rather than be vile and noisome by themselves? For that is not to be called consent; seeing that we do not approve what they do, always wishing that they would not, and, as much as in us lies, hindering them that they should not do it, and, when it is done, not only not committing it with them, but with all possible detestation condemning the same.
Source: On Lying (New Advent)