After his discussion of whether it’s a sin to kill plants or animals, Thomas discusses the question of whether it’s permissible to kill sinners. Thomas says it is not a sin to kill sinners. We’ll see that the question of killing sinners is importantly related to the question of killing animals.
I don’t know about what others think, but at first glance this seems like a strange discussion to have. So my first question is why Thomas thinks he needs to consider the question of whether it is a sin to kill sinners. (I suppose there could be (and probably are) some aspects of Thomas’s historical and cultural setting that would suggest this topic to him, but I don’t know about them.) I think what is off-putting is the question of whether it’s permissible to kill sinners. In a secular society such as ours, “sinner” is not a category that comes to mind for “people who we might have a question about whether it’s permissible to kill.” We would rather categorize such people as “criminals,” which is a much smaller class. For Thomas, I think, all criminals are sinners, but not all sinners are criminals. (Thomas reminds us in this article that “whatever is forbidden by God is a sin.”)
Perhaps it also helps to note that Thomas is concerned in this article with the question of whether it is permissible to kill sinners. The question is not whether we are (or at least someone is) obligated to kill all sinners.
Thomas poses and responds to three objections to the claim that it’s permissible to kill sinners. I’ll go over the first and third. The first objection is that in the parable of the wheat and cockle (Matthew 13), God forbids uprooting the cockle. So, God forbids killing sinners.
Thomas’s response is that the parable only forbade the uprooting of cockles because that action would harm the wheat. So God only forbids the killing of sinners when nonsinners would be harmed by that action.
The third objection is that it’s evil in itself to kill a human being. (Both Augustine and Aristotle back this claim up.) We should instead have charity for all human beings.
Thomas’s reply to this is that a human being who has sinned “departs from the order of reason, and consequently falls away from the dignity of his manhood, in so far as he is naturally free, and exists for himself, and he falls into the slavish state of the beasts, by being disposed of according as he is useful to others.” That is, it’s permissible to kill a sinner because the sinner is in an important sense no longer a human being.
Here’s one point where I think Thomas’s position is interesting from our point of view: Thomas says it’s permissible to kill a sinner because the sinner is no longer a human being but is instead merely an animal—in fact, is worse than an animal. Since it’s permissible to kill an animal for our use, it’s permissible to kill a sinner for our use. (So note that if Thomas’s argument that it’s permissible to kill animals doesn’t work, this argument won’t work either.)
But in what sense could killing a sinner be “for our use”? Here’s another point where Thomas’s position is interesting: He does not make any mention of rights in this discussion. Instead, he puts the whole discussion in terms of the health of the community, and he relies on the Aristotelian principle that “every part is directed to the whole, as imperfect to perfect, wherefore every part is naturally for the sake of the whole.” Individual people, according to Thomas, stand to their community as a part to its whole. If a part causes harm to the whole, then for the sake of the whole the part should be cut away. Thus, if a person is “dangerous and infectious to the community, on account of some sin, it is praiseworthy and advantageous that he be killed in order to safeguard the common good.”
There is in Thomas’s discussion of killing sinners no talk of rights, only principles about parts and wholes and the health of the community.
