In a world corrupted by darkness and evil, he who wants to preserve balance will end doing the good.

Its gotten to the point where people will hate the Lore just because its popular to do so. Yes, we've had some with poor lore, but frankly, people won't even read it, and instantly go into hate mode.

There are a couple problems with your theory. First of all, the box was hidden away for 200 years, this is proof enough it was not critical to the balance in any way shape or form. Secondly, the ninjas as others have stated are good AND evil.

The master intentionally going in to die is far fetched. I imagine he knew he might die, but he also might have thought Zed would change. The problem is that we can't draw logical conclusions from what is given, you HAVE to stretch it out to fit into a reasonable state which is part of the problem.

This is assuming the world is corrupted by darkness and evil. Demacia is a shining beacon of justice, along with other champions like Kayle or Ashe. The kinkou tip the balance very slightly in whichever direction is required.

A good videogame comparison might be third echelon from the splinter cell series. They may not always do what is right, but they do what is needed. Or they used to before conviction, but the point stands.

"StarkRavenMad" complains about people raging. Sorry, just had to make note.

You are all thinking too much about this. The box is knowledge of ancient forbidden ninja techniques. Think of Mangekyo Sharingan Scroll that Itachi found. Same thing. Zed was banished, came back to retrieve the power again because his was incomplete. The speculation to why Zed screams? I believe because of certain context in the story that the master had either destroyed the box or hidden it from Zed, thus incurring his wrath. The whole nonsense with him being some counter to Shen and balance is thinking too much and raw speculation.