It is a little galling having the Organians equating the Klingons and the Federation as if there's no difference in how each side uses violence.
The thing is the Organians are correct in their action that they're trying to prevent mutually assured destruction between two parties. It doesn't really matter which side is "more" moral if the result is literally millions or billions of deaths. Not just the Klingons will die in the battle but all the people they have enslaved and conquered. The Federation is more concerned with justice than peace.
The Excalbians appeared to feel good and evil were a matter of perspective and that both used similar methods to achieve their goals. Thats simplistic, but when the battle is joined both sides do employ similar methods.
The Organians were obviously not menaced in any way by the Federation or the Empire so why did they feel the need to interfere in their conflict? They could have sat back and simply observed the two sides fighting it out like two warring colonies of ants.
Yes, but they intervened on moral grounds by enforcing a peace treaty.