If humankind never sees the golden dawn of world peace it will not be because the quest was too whimsical or idealistic, but because each of us pursued universal principles in our own way, and only when it was to our own advantage.
We now consider due process for prisoners of war to be an unaffordable luxury. Even the most progressive of souls seems to feel that world peace under the rule of international law was a childish whim from some fantasy planet, and that violence is the only sane tool for organizing this one.
When we punished the war criminals of WW2 for doing some of the same things we now defend, we did not deem those standards to be unrealistic ideals, but the very underpinnings of civilization itself. If the world never sees a day of peace it will not be the principles that failed, but we.