This question really is a no-brainer. It’s wrong to kill innocent people, right? Right. On a question like this, the answer isn’t surprising, so we need to pay attention to the reason why Thomas thinks it’s wrong to kill an innocent person.
The basic distinction Thomas makes (and, remember, he always makes a distinction) is between a man considered in himself and a man considered in relation to others. If we thought about everyone simply in terms of what each person is in himself, Thomas says it would be unlawful to kill anyone because killing a person would destroy the nature that God made. What makes killing another person lawful is taking into consideration the relation that each individual bears to the community. If a person has sinned, which is a state Thomas has already considered, then it is lawful to kill them to preserve the common good. But if a person is just, then it is not lawful to kill them because such a person preserves the common good; in fact, such a person is “the chief part of the community.”
Thus, Thomas’s basic reason for saying it’s not right to kill an innocent person is that (1) such a person has done nothing to harm the common good and (2) such a person in some sense is an important part of the common good.
Since the answer to the question is plain, the objections that Thomas addresses are in some sense sophistical. One objection concerns a hypothetical judge who, being bound by the rules of judicial procedure to accept the testimony of false witnesses, condemns a man to death on the testimony of those false witnesses knowing that the condemned is innocent. What should the judge do? Thomas says: cross-examine the false witnesses as carefully as possible in order to reveal their bad motives. If that doesn’t work, send the case to a higher authority. If that doesn’t work, follow the rule of the law and condemn the innocent man—but knowing in this case that the false witnesses and not the judge have condemned the man wrongly.
If that objection doesn’t move you, try this one: If you kill an innocent person, that person goes to heaven. If you kill a guilty person, that person goes to hell. So, better to kill an innocent person, right? Wrong. You should not follow this reasoning for four reasons: (1) You should love the just man more. (2) The just man is less deserving of injury than the guilty. (3) You deprive the community of a greater good. (4) You despise God (on the basis of Luke 10:16).
If that objection doesn’t move you, perhaps the next one will touch your Kierkegaard-loving soul: What about Abraham, who was willing to kill his innocent son? Thomas will have none of Kierkegaard’s (or, really, “Johannes de silentio’s”) worrying: If Abraham had killed his innocent son, he would have done nothing wrong because he would have been following God’s command. And whatever God commands in matters of life and death is right. End of story.
I think what we see in Thomas’s reasoning about killing the innocent is a consistent dependence on the appeal to the common good. You shouldn’t kill an innocent person because that person “preserves and forwards the common good.” He does not appeal to an argument that appeals to the image of God in a person. In fact, if I understand him correctly, such an argument would conclude that we shouldn’t kill anyone. Killing the guilty is only justified by appealing to the harm they cause to the common good.
