I don't mean to suggest that there is no justification for punishing people beyond forcing them to compensate the victims of their actions. It does seem like it might be fair to impose a penalty on someone for violating the rights of others. But it occurs to me that using punishment as a way to deter future rights violators is very obviously a way of using someone as a means to an end. Accordingly, it seems like a just society would not allow punishment of that sort.
One might wonder why I would make a big deal out of this, given that I've admitted that there could be other justifications for punishing people. What I have in mind is Nozick's idea that we apply certain labels to the reasons for particular arrangements, and that we might drop the labels if presented with alternative reasons. So if the only reason we could possibly come up with for punishing someone in a certain instance were that doing so might deter future people from repeating her offense, then I would contend that such a punishment would be unfair, because it would sacrifice her in order to achieve our ends.
It seems that I should make a distinction between established penalties and ad hoc punishments, though I'm not sure that this distinction is exactly the one which is making me feel unsure of myself. What I'm thinking is this: it would be perfectly fair to say that "Anyone who breaks this rule will be punished significantly on top of being forced to compensate any victims." Such a rule would clearly be a deterrent, and it would be using punishment as a way to deter people. But it doesn't seem disrespectful.
The sort of deterrent I'm calling illegitimate is where someone is being made an example of, in spite of the fact that she clearly doesn't deserve the punishment she's getting. Could there possibly be any reason that would justify this sort of punishment without being subject to the objection I've raised?
I can think of one response to what I've said here, which is that by violating the rights of others, a person forfeits a claim to respect. A good example of this comes from Locke: "In transgressing the law of nature, the offender declares himself to live by another rule than that of reason and common equity...and so he becomes dangerous to mankind, the tye, which is to secure them from injury, being slighted and broken by him. Which being a trespass against the whole species, and the peace and safety of it, provided for by the law of nature, every man upon this score, by the right he hath to preserve mankind in general, may restrain, or where it is necessary, destroy things noxious to them, and so may bring such evil on any one, who hath transgressed that law, as may make him repent the doing of it, and thereby deter him, and by his example others, from doing the like mischief" (Section 9).
Locke's claim seems to contain a bunch of different points. The first is clearly that by violating the rights of others, a person forfeits the right not to be harmed. I don't object to that. The second is that people have the right to punish the offender, because they have the right to preserve mankind. I'm not sure I agree with this line of reasoning, because it seems to want to use the offender in order to achieve social ends, which makes me uncomfortable. To be clear, I'm not disagreeing with the claim that we have the right to punish an offender; I'm only unsure whether I think that the source of this right is our right to do what is necessary to preserve mankind. But my disagreements do not impact the validity of conclusion of the second point, we can safely move on.
The third point is that we have the right to punish an offender to the point of making him repent what he has. I think this is right, though again I'm not sure I agree with how Locke got there. But the movement from the third point from the fourth point is what really interests me. The fourth point is that others will be deterred by the repentance of the offender. I like this way of thinking about it a lot.
So taking this into account, it seems like we could say that we are justified in punishing an offender beyond what's necessary for compensating the victim to the point of causing the offender to be repentant for his transgression. And because of this, we would be able to deter others from committing the same act in the future, because others would see that they would be punished to the point of repentance as well if they offended. But it seems like we could simultaneously say that we would not be justified in punishing someone far beyond the point of repentance in order to even further deter others. I think I'm pretty happy with that.