There is a certain strain of thought that I have had for some time. That the ultimate justice that can be inflicted is for them to truly understand why what they did was wrong, how it hurt people, and how it was baseless, senseless, or otherwise selfish beyond acceptance. This is the 'ultimate justice' only in cases where remedial action isn't possible, and all that remains is ensuring that it doesn't happen again.
The human conscience is a fragile thing, and there's so much self image connected to it that it tends to live in a deluded place, or at least that's how my brain tends to gravitate when considering myself and my place here, what it means, and what I mean to the people who I am an element of their lives, from a face that was seen once, to actual real familiarity and intimacy. It's not that I think that I should be focused on the judgement of others, it's more considering what actions are just. What role am I playing in their story.
Consider a hunter that believes that the ritual of hunting must include making sure that animals aren't left to suffer wounds over a protracted, terrible death. Imagine being an animal, stunned, barely sensate, your brain is misfiring and you can barely make sense of the world around you. You know that you are hurt, you know that you are likely to die soon. But for this moment, you are too overwhelmed to be aware of the pain or the bleeding, and as the hunter steps closer, your eyes may not even focus on them, maybe you hear whatever mechanical actions are involved in readying their weapons. A click, and before the sound hits your brain you are killed. And fragments of your awareness putter off into gasps of nothingness, whether snuffed by the direct action of mechanical destruction of the bullet or the lack of oxygen as the heart stops pumping.
Consider being the hunter, having the understanding of the experience the animal had. The mad fear and dash before the wound caught up with the animal, the frantic desperation continuance that you impinged upon. Consider yourself as the vague vision in the animal's last memories, knowing that what you did caused the pain that you are experiencing as the animal. Would you be able to live with yourself knowing the suffering that you caused, the threads of a consciousness that has most of the same emotions as you do dissolving into noise cascading around the stultifying chemical soup of the animal's brain, are you okay with being that agent in that story if you had to live the interaction with the animal?
What divine well of power gave you the right to take away awareness from another being?
But if we continue down graduations of seriousness of 'sin', what of the plants that you eat? What about the trees cut down for your house? What about the people whose potential low cost housing wasn't built because your luxury neighborhood was? What about that African who mined the cobalt in your phone, a dangerous and dirty job, which they were likely forced into by violence or poverty?
The structure of this understanding is near total understanding of thousands and thousands of lives and how they changed in crossing your path and being subjected to your actions. It seems likely that to experience this kind of justice, you would accrue knowledge of everything in the universe that your actions touched.
But we can't live in this kind of justice. Experiences are private, impossible to transmit without huge losses of information. And when when that is corrected for, the experience of the feelings that caused each action are as ephemeral as the charges in the synapses themselves. Your emotions in each moment are ultimately the motivations for each action.
We do not live in a universe that permits panopticons or omniscience. We live in a universe where radiation scatters information into impossible pieces.
So justice must be the process of improving the environment of the future, for setting up a garden of actions that bloom for each other in a pleasing and harmonious way. But we live in a universe which is hostile to systems that are highly ordered, and there is noise in every computation, every bit of nucleotide copied, every action taken. On top of that, systems aren't static, and when they're computational as lifeforms tend to be, even the rules tend to change over time as the composition and structure drifts.
The universe is hostile to self-perpetuating utopias because they, as all complex energy using entities, ride the crest of equilibrium of rising and falling energies, and such energies deplete or change the environment over time. There will always be conflict because the system is constantly falling apart even as it is erected anew and that means that even if niches are overall stable, there is a constant turnover of where those niches are and what forms they take.
Humans, and other entities on the same scale(presumably), cannot depend on generational stability because their exploitation of the environment is so successful that it depletes land faster than it can recover, on top of that they aren't able to enter into estivation to permit recovery while preserving energy stores. This is why ancient humans were nomads, as were many large omnivores at various points.
We are therefore probably doomed to live in a world where conflict is inevitable, omnipresent, and happening on all scales. But in our lives, we have the choice to blunt the conflicts, to build a bubble where such things aren't important on the scale we have to live in most of the time, but that cannot fix the problems on the larger scale. Perhaps such places may incubate the attitudes required, the clarity to see the invisible systems that can be disrupted, and the determination to make the world a fairer place. Or they don't, and the self absorption closes in until the world burns down around you and disperses the idea of independence like the fallacy that it is, given the whole response to climate change thus far this is looking very appealing.
But it's hard to live under the other possibility, that you're doomed. That you can't do anything without overturning all the systems around you, and that in the end, the Midwest will be the American wasteland, a place of paltry use and full of farmers out of work as the increasing heat bakes the fragile water cycle. The systems that oppose change are immense and well funded, and they have already started drawing lines on the scarce resources of the future, so that their hand will still have the say regardless of how terrible the externalities of their actions are. Just look at those water futures.