The war to end all wars is not possible, for you cannot end anything that is wrong in and of itself, by doing that very same thing, no matter, what justification is claimed in order to do so. While self-defense in any of its many forms has its place, seldom is such self-defense limited to true self-defense, rather, in most cases, self-defense is proclaimed, but in action, it is not actually self-defense, but merely another form of war, mislabeled and misidentified by the practitioner as self-defense.
So too, this means that those that believe that certain crimes must be punished by killing that person in cold blood by utilizing state resources, as if this act of state sanctioned murder, though not called that by the state, is somehow justified, is absolutely senseless. You cannot end murder by the act of murder, just as you cannot end thievery by being a thief, nor can you end hatred in any of its many forms, by being hateful, and so on and so forth.
The very things that are wrong right now by some agent to do, cannot ever be corrected by doing in essence the very same things as long as it is sanctioned or justified somehow by the state, as if this will put everything right, for it will not, it might end a particular bad deed at that time, but it will not fundamentally and morally correct the causes of it and it is not an appropriate answer to wrong actions. Fundamentally, you cannot produce peace by the sword, or justice by the hangman's noose.
The reason that so many people don't believe in the type of justice that is not retributive justice, is because they don't believe that turning the other cheek, or that non-resistance to evil, or that the giving up of one's cloak, could possibly be the correct response to wrongdoing in the real world. That is to say, they might agree with Christian philosophy in a house of worship, or while watching a movie or while reading a book with that narrative and theme, but the actual return of good to evil is more akin to a fairytale, as this world is filled with very bad people that will stop at nothing, and, therefore have to be dealt with forthrightly.
As you might expect, when it comes to judging oneself, most people are rather generous towards themselves and their loved ones, and far less so, when dealing with others, especially when those others don't look, respond, or act the same as they do, making it rather easy to judge them from a supercilious vantage point, but that sort of judgment is flawed, for having not lived in another person's shoes, you really don't know much about that person, and certainly not enough to be ethically permitted to render judgment upon them.
In reality, the time to turn your swords into plowshares is not after you have killed off all of your enemies, but when you recognize, that you have no enemies in the first place, for if you can take your enemy, and turn that enemy into your friend, than you have gained a friend, while losing an enemy, and that fundamentally is the very thing that needs to be accomplished in order to bring lasting peace and justice to this world.