Also, let’s face it, it gives a decent reason not to want to send Princess Luna. I love you sis, you mean the world to me, let’s just not put you in a situation where you’re going to be required to access your reserves of hate and anger for power, hmm?
OMG, she used that same dark magic in Princess Twilight Sparkle Part 1.
It sure as hell better have some sort of consequence.
“Oh right, these crystals change when charged with pure malice. Just let me channel a little HATRED AND CRUELTY from the depths of my soul. No biggie.”
You scare me Sparkle.
What if they tried that the first time, and that’s what trigged Luna turning into NMM?
And the nature of the test was to make sure that WOULDN’T happen with Twilight, before they gave her more power?
…What if Hatred and Fear is another leyline of emotional magic, and Sombra was the first to tap into it, gaining his status and going mad in the process?