I'm afraid i'll have to say that justice is essentially still harm. Imprisonment, that is, seclusion from interacting with society, has noticeable harmful effects and intents -- it is executed under the belief that the threat of sanctioning will dissuade the criminal and other citizens from repeating the crime.
In essence, the only factor that differs justice from vengeance is formal legitimacy -- the former is carried out by legitimate institutions of state, the latter by individuals and groups acting outside the frame of legality (be it sanctionable or not). Accusing non-state-sanctioned vengeance of causing discord is redundant considering how little prisons, as institutions, can prevent criminal activity from happening in society and many times even within the very walls of the prison.
You mentioned vengeance being subjective. Assuming you agree with me that justice is only legitimized vengeance, what ensures that a state will be 100% impartial in a procedure of judgement? You can amenize the most extreme inpulses of vengeful feeling by state mechanisms and formalities, but at the end of the day, where's the guarantee that the judge will be the enlightened ultra-ethical figure the state and society expect them to be?
What i'm trying to say here is that the issue is not a question of legality, but ethics. "Our (my?) Ideal Grant" could not have just rammed his bills and reforms for racial and class equality through a potentially hostile government, but that is more an issue of the forces and pressures making such reform unlikely. Southern society (be it the WASP planter or the poor white farmer with incomplete civic education), as it was not fully re-educated towards less asinine political ideals, represented a pressure actor. These pressures could have been dissuaded by educating the younger generations (which is not a necessarily authoritarian ordeal -- Paulo Freire details how it can happen without symbolic violence), but alas, this is one of the areas in which the US government might have failed.
I agree that what
you are discussing it is a matter of ethics. Several points though:
-- The actual discussion of this thread is
not one of ethics, since "what would make Grant be perceived as a great President" isn't an ethical question, so you insist on having the wrong discussion. I have already pointed that out a few posts back.
-- I disagree with your view of justice, which is basically a form of legal positivism. That is but one view, but it is certainly not mine.
-- In fact, I received my doctorate by arguing the exact opposite, namely that man-made laws are irrelevant to the nature of justice, and can at best co-incide with it, or (more likely) vaguely approximate it.
-- In my view, justice by definition precludes "punishment", as justice is only concerned with producing
eudaimonia. If this requires that a dangerous person be locked up, then this must be done; but not to avenge, but to prevent him from doing further harm. (And if he is not going to do further harm, locking him up to "punish" him is pure madness, since it would preclude him from doing good. Much better would be to sentence him to repairing or compensating any damage he has done, as best as can be managed.)
-- This doesn't imply that acts of revenge, borne of emotion, cannot be justif
ied, since they certainly can. But that we understand an act does not make it the ideal act. Justice is the ideal act.
-- In this, justice happens to perfectly align with the needs of society as a whole (i.e. peace and reconciliation), since its execution will tend to foster further co-operation, and bring greater peace to all. Vengeance, contrarily, can only cause further division. (Which, while pleasing to those who are vengeful, would ultimately bring harm to yet other innocents-- who do not deserve this.)
-- Essentially, you must ask: is my enemy not
perfectly defeated when I make him into a friend? And would seeking vengeance not primarily serve to embitter my enemy, thus ensuring that he will never be my friend, which implies that any final defeat of him will be much later and at a much higher cost, if it even arrives at all?
-- And once you ask that, you will know that it is only sensible to fight enemies who remain a threat. Already defeated enemies must be either butchered (if you are a vile monster who does such things) or made into friends (if you are a human being, and worth that name). Justice demands this of us. And even when we ignore justice: the essential needs of a divided, post-war society demand it, too.
As such, both my sense of justice and my appraisal of the needs of a society emerging from a civil war tell me, very clearly, that the best option is to forego all desires for vengeance. (This is sound advice in any event, since a logical analysis will tell you that vengeance is never constructive and always harmful. Not only to its targets, but also to you-- and to all of the community in which you exist.) This makes the requirements for a succesful Grant presidency abundantly obvious to me.