You're assuming that there's some morally-right group that could make those decisions? That's the problem. Corruption starts from the top. Who is to say who is or isn't "purely just"? And even if someone claims to be able to determine as much, who is to say that they themselves are "purely just" and wont just let a bunch of corrupt people have the power?

Down the chain, someone has to be truly just for the rest of the powers beneath them to be just. Just as corruption starts from the top, the opposite is true. Except humans are inherently corrupt. A lot of people remedy this by claiming that at the top is God, who is obviously "purely just." Except if God doesn't exist, the opposite is true (that a human, susceptible to corruption and sin, is at the top and naturally the lower powers follow suit.) Which is exactly why religion is so dangerous. It gives this divine label to God, or Allah, or whoever else, but in reality they don't exist and some corrupt, or at the very least ignorant, human is calling the shots.*

*Edit: And while they're calling the shots, they're hiding behind a facade that they're actually doing the bidding of God, and anything they say is really the word of God. And thus, they are infallible.